EVOLUTION, 


RACIAL   AND    HABITUDINAL 


BY 


Rev.  JOHN    T.  GULICK. 


Washington,  D.  C.  : 

Published  by  the  Carnegie  Institution  of  Washington. 

August,  190s. 


UNIVERSITY  FARM 


EVOLUTION, 


RACIAL   AND    HABITUDINAL 


BY 


Rev.  JOHN   T.  GULICK. 


Washington,  D.  C.  : 

Published  by  the  Carnegie  Institution  of  Washington. 

August,  1905. 


CARNEGIE  INSTITUTION  OF  WASHINGTON. 
Publication  No.  25. 


PRESS    OF   GIBSON    BROS. 
WASHINGTON,  D.  C. 


P  R  E  F  A  C  l^ . 


In  the  present  volume  I  have  brought  together  in  one  connected 
presentation  the  chief  results  of  my  investigations  cQUcerning  the 
factors  of  organic  evolution.  Portions  of  my  theory  of  divergence 
which  were  published  in  the  Ivinnean  Society's  Journal  are  repro- 
duced in  the  Appendix,  with  careful  revision;  but  the  fullest  exposi- 
tion of  the  fact  that  all  evolution,  as  we  now  observe  it,  is  divergent, 
and  that  other  factors  besides  natural  selection  are  absolutely  neces- 
sary both  for  the  origin  and  the  continuance  of  this  divergence,  is 
given  in  the  new  chapters  constituting  the  body  of  the  volume. 
These  chapters  have  been  written  while  considering  the  most  recent 
biological  investigations  bearing  on  the  general  theory  of  segregation. 

The  first  four  chapters  of  the  volume  are  introductory,  in  that  they 
present  many  facts  of  divergence  and  distribution  in  both  natural  and 
domestic  species,  which  remain  complete  enigmas  till  the  forms  of 
racial  and  habitudinal  segregation  have  been  fully  recognized.  Chap- 
ters V,  VI,  and  VII  present  the  fundamental  laws  of  segregation,  and 
the  interaction  between  the  different  classes  of  factors — between 
isolation  and  selection,  between  racial  segregation  and  habitudinal 
segregation,  between  autonomic  factors  and  heteronomic  factors. 
In  Chapter  VI,  §  II,  14-17  (pp.  loi-iii),  will  be  found  a  fuller  exposi- 
tion than  has  been  presented  in  any  of  my  essays  published  by  the 
lyinnean  Society,  of  the  tendency  of  certain  combinations  of  partially 
segregative  endowments  to  become  more  intense  in  successive  genera- 
tions. It  is  shown  that  this  is  especially  the  case  when  endowments, 
tending  toward  the  mating  of  like  forms  with  each  other,  are  reinforced 
by  varying  degrees  of  mutual  infertility  and  incompatibility  between 
'unlike  forms.  Appendix  II,  §  IV,  3  (pp.  241-243),  briefly  indicates 
several  methods  of  constructing  what  I  have  called  the  permutation 
triangle.  It  was  first  constructed  in  order  to  show  that  the  sterility  of 
cross-unions  between  divergent  forms  (whether  they  be  varieties, 
species,  genera,  or  higher  groups),  would  lead  rapidly  to  the  extinction 
of  most  of  these  forms,  if  instincts  and  other  endowments  did  not 
facilitate  the  union  of  compatible  forms.  The  table  thus  constructed 
is  foimd  to  be  a  concise  presentation  of  certain  classes  of  probabilities 
that  arise  in  the  pairing  of  things  by  chance. 


^^0\ 


IV  PREFACE. 

The  principles  molding  segregation,  and  so  controlling  variation 
and  heredity,  and  the  effects  on  racial  and  social  evolution  produced 
by  such  control,  are  presented  with  considerable  fullness  of  illustra- 
tion on  the  biological  side.  For  my  purpose  it  did  not  seem  necessary 
to  dwell  at  equal  length  on  the  social  aspects. 

Another  broad  department  of  the  subject  is  referred  to  in  only  the 
briefest  way.  This  is  the  effect  of  amalgamation  or  regressive  segrega- 
tion, both  racial  and  social.  I  have,  however,  pointed  out  that  in  the 
history  of  man  segregation  was  the  leading  factor  through  countless 
generations  when  races,  languages,  and  institutions  were  becoming 
increasingly  subdivided ;  and  that  it  is  only  in  modern  times  that  the 
barriers  to  free  intercourse  have  been  so  rapidly  yielding  that  regres- 
sive segregation  has  been  the  predominant  feature  in  human  history. 

I  have  presented  evidence  that,  even  in  the  case  of  invertebrate 
animals,  members  of  the  same  species,  exposed  to  the  same  environ- 
ment in  isolated  groups,  will  often  arrive  at  divergent  methods  of 
dealing  with  the  environment,  and  so  subject  themselves  to  divergent 
forms  of  selection.  If  my  contention  is  in  accord  with  the  facts,  the 
assumption  which  we  often  meet  that  change  in  the  organism  is 
controlled  in  all  its  details  by  change  in  the  environment,  and  that, 
therefore,  human  progress  is  ruled  by  an  external  fate,  is  certainly 
contrary  to  fact. 

It  is  of  no  little  interest  that  the  recent  developments  of  biological 
science,  in  both  Europe  and  America,  are  pointing,  not  only  to  the 
power  of  the  organism  to  deal  with  the  same  environment  in  different 
ways,  and  so  to  determine  the  forms  of  what  I  have  called  active  (or 
endonomic)  selection,  but  also  the  power  of  many  animals  to  deal  with 
sudden  changes  in  the  environment  in  such  a  way  that  the  group  is 
saved  from  extinction  till  ''coincident  variations"  have  time  to  arise, 
insuring  completer  adaptation  to  the  new  conditions  through  selection. 
The  teachings  of  biology  are  thus  coming  more  nearly  into  accord 
with  that  school  of  sociology  which  has  for  years  maintained  that  the 
social  group  may  learn  to  determine  the  form  of  its  own  social  evolu- 
tion. We  are  thus  led  to  hope  that  man  will  in  time  determine  his 
own  evolution,  racial  as  well  as  social ;  for  when  sufficiently  advanced 
to  realize  the  breadth  of  the  responsibilities  resting  upon  him,  the 
form  of  his  racial  inheritance  will  naturally  be  determined  by  the 
ideals  shaping  his  social  organization. 

In  the  third  chapter,  and  again  near  the  end  of  the  last  chapter, 
attention  is  called  to  the  fact  that,  in  accommodational  and  anticipa- 
tory action,  and  in  cooperation  for  the  attainment  of  future  results, 
all  forms  of  life,  from  the  earliest  protozoa  till  we  reach  the  highest 


PREFACE.  V 

types  of  spiritual  life  in  man,  present  activities  entirely  unknown  in 
the  inorganic  world.  In  the  degrees  of  attainment  reached  in  coope- 
rative action  (with  the  division  of  labor  and  community  of  interest), 
and  in  anticipatory  and  discriminative  action  (securing  adaptation 
to  future  conditions),  we  find  a  definite  test  of  the  stages  of  evolution 
reached— a  test  that  is  applicable  to  the  lowest  as  well  as  to  the  highest 
living  creatures. 

Of  my  papers  previously  published,  the  one  on  Divergent  Evolution 
has  received  the  most  attention.  This  is  perhaps  due  to  the  fact  that 
it  was  not  only  published  in  London  in  the  Linnean  Society's  Journal 
for  1887,  but  was  reproduced  in  this  country  in  the  report  of  the 
Smithsonian  Institution  for  1891.  I  wish,  however,  to  emphasize 
the  importance  of  the  factors  enumerated  and  illustrated  in  the  one 
on  intensive  segregation  (see  Appendix  II).  If  we  would  fully  com- 
prehend the  factors  producing  the  segregation  of  organic  types,  we 
must  recognize  not  only  the  forms  of  isolation  by  which  groups  are 
first  set  apart ;  but  also  the  physiological  and  psychological  forms  of 
segregation  by  which  the  slightly  divergent  forms  are  held  perma- 
nently apart,  and  still  further,  the  factors  producing  divergence  in 
these  isolated  groups,  and  so  resulting  in  intensive  segregation.  I 
show  that  intensive  segregation  is  due  not  only  to  the  exposure  of 
isolated  groups  to  different  environments,  but  also  to  the  different 
methods  of  dealing  with  the  same  environment  adopted  by  the  iso- 
lated groups.  I  also  point  out  other  factors  that  are  subject  to 
change  without  any  change  in  the  activities  lying  outside  of  the 
species;  and  all  such  I  class  as  autonomic  factors.  Throughout  all 
the  chapters  the  underlying  purpose  has  been  the  investigation  of  the 
autonomic  as  well  as  the  heteronomic  factors  controlling  evolution. 

The  chief  hindrance  to  the  increase  of  our  knowledge  of  the  method 
of  evolution  is  the  tendency  to  regard  some  one  of  the  several  prin- 
ciples influencing  segregation  as  the  one  principle  controlling  the 
whole  process.  I  believe  Prof.  H.  F.  Osborn  makes  no  mistake  when 
he  suggests  that  the  ruling  method  of  the  next  important  advance  in 
the  interpretation  of  evolution  must  be  one  recognizing  the  complex 
action  of  diverse  principles,  and  at  the  same  time  grasping  the  under- 
lying unity  of  the  process.  In  the  present  volume  the  question  is 
raised  whether  segregation,  with  its  controlling  influence  in  the 
spheres  of  both  racial  and  habitudinal  evolution,  is  not  the  underlying 
principle  we  are  seeking.  It  must,  however,  be  carefully  noted  that 
segregation  as  defined  in  this  volume  covers  a  much  wider  sphere 
than  isolation.  In  order  to  reach  the  more  pronounced  results  of 
racial  segregation,  the  separate  groups  produced  by  isolation  must 


VI  PREFACE. 

for  several  generations  be  subjected  to  divergent  forms  of  selection ; 
and  in  all  the  forms  of  animal  life  that  are  capable  of  learning  by 
experience,  accommodation,  controlled  by  the  principles  producing 
habitudinal  segregation,  is  constantly  guiding  and  shaping  racial 
segregation. 

Though  more  familiar  words  have  been  chosen  for  the  title  of  this 
volume,  the  subject  here  treated  would  have  been  clearly  expressed 
if  the  title  had  read :  ' '  Habitudinal  and  Racial  Segregation ;  or,  the 
origin  and  intensification  of  organic  types,  guided  by  innovation  and 
tradition  acting  under  segregate  association,  and  established  by 
variation  and  heredity  acting  imder  segregate  intergeneration." 

John  T.  Guuck. 
Oberun,  Ohio. 


CONTENTS. 


Chapter  I. — ^Introduction. 

Facts  Calling  for  Explanation 1-3 

Small  Areas  of  Distribution  for  Species  of  Hawaiian  Snails i 

The  Intergrading  of  Species 2 

Selection  not  Always  the  Cause  of  Divergence 3-6 

In  Many  Cases  Sexual  Selection  not  the  Cause 3 

In  Many  of  the  Same  Cases  Natural  Selection  not  the  Cause 4 

May  not  the  Prevention  of  Free  Crossing  be  an  Explanation 6 

Investigation  of  Causes  and  Effects  of  Segregation 7 

Segregation  the  Unifying  Principle  in  Evolution 7 

Chapter  II. — Bionomic  Laws. 

Method  of  Investigation 9-13 

Scope  of  Bionomics 9 

Why  we  Commence  with  the  Method  of  Evolution 9 

Need  of  Investigation  of  all  Factors 10 

Natural  and  Sexual  Selection  not  the  Only  Factors 11 

Comparison  of  Conditions  in  Natural  Species  and  in  Domestic  Varie- 
ties    12 

Production  of  Domestic  Races 13-22 

Continuance  of  Races 13 

Transformation  of  Races 14 

Divergence  of  Races 17 

Stability  of  Races 19 

Amalgamation  of  Races 20 

Influence  of  Acquired  Characters  on  Racial  Characters 20 

Chapter  III. — The  Evolution  of  Natural  Species. 

Unity  and  Diversity 23-29 

Darwin's  Explanation  of  Unity 23 

Divergence  Through  Variation  under  Isolation  and  Unity  Through 

Community  of  Descent 24 

Facts  in  Distribution  of  Hawaiian  Snails 26 

Diversity  of  Natural  Selection  not  a  Sufficient  Explanation 27 

Divergence  through  Independent  Transformation 28 

Natural  Selection  as  Explanation  of  Evolution 29-34 

What  Natural  Selection  does  not  Explain 29 

Selection,  how  Far  Determined  by  External  Nature 31-34 

Discontinuity  of  Species 34~36 

Chapter  IV. — Divergence  Under  the  Same  Environment. 

Explanation  of  Plate  1 37 

Explanation  of  Plate  II ; 39 

vii 


VUl  CONTENTS 

Explanation  of  Plate  III 41 

Oahu  the  Metropolis  of  the  Achatinellidae 42 

Plate  A.     Map  of  the  Hawaiian  Islands. 

Plate  I.     Eight  Genera  of  Achatinellidae. 

Plate  B.     Map  of  Oahu,  Hawaiian  Islands. 

Plate  II.     Twenty-five  Species  of  Achatinella. 

Plate  III.     Variation  and  Intergrading  of  Bulimella. 

Explanation  of  Plate  B 43 

Chapter  V. — The  Four  Segregative  Principles. 

Racial  and  Habitudinal  Segregation 45-50 

Interaction  of  Acquired  and  Inherited  Characters 45 

Segregation  a  Fundamental  Law 47 

Segregate  Association 48 

Interaction  of  Racial  and  Social  Factors 49 

Determinate  Evolution  of  Evolutionary  Terminology 50 

Segregation  the  Combined  Result  from  Four  Principles 51-55 

Racial  Segregation  Controlled  by  Two  Principles  and  Habitudinal 

Segregation  by  Two 51 

Importance  of  Isolation 51 

Definitions  of  the  Four  Segregative  Principles 53 

Objections  to  the  Terms : 54 

Interaction  of  the  Four  Principles 55-78 

Repeated  Action  of  One  or  Combined  Action  of  Several  Principles .  .  55 

Importance  of  Each  of  the  Principles 56 

Two  Methods  of  Generalization 58 

Change  of  Tradition  in  Chimney  Swift 59 

Variation  and  Accommodation  Two  Methods  of  Adjustment 59 

Conditions  Suddenly  or  Gradually  Encountered 60 

Accommodation  in  Man 61 

Endonomic  Selection 63 

Coincident  Selection 64 

Endonomic  and  Coincident  Selection  Contrasted 65 

Coincident  Selection  Illustrated •. 66 

Endonomic  and  Coincident  Influences  Defined 66 

A  Colony  of  Cats  with  Aquatic  Habits 67 

Structural  Isolation  and  Structural  Selection  Illustrated 68-70 

Young  Snails  with  Reverse  Coil  from  that  of  Parents 70 

Mutations  and  Varieties 71 

Theories  Compared 72 

Degeneration  with  Cessation  of  Selection 73 

Degeneration  in  Eye-sight  and  its  Lessons 74 

Degeneration  in  Breeding  Instincts 75-76 

Mutation  as  Recently  Pvxpounded  by  De  Vries 77 

Selection  and  Inheritance  of  Acquired  Characters 78 

Chapter  VI. — Analysis  of  the  Four  Principles  op  Segregation. 

Chief  Divisions  of  the  Four  Principles 79-81 

Six  Conditions  on  which  Racial  Evolution  Rests 79 

Six  Conditions  on  which  Habitudinal  Evolution  Rests 80 


CONTENTS.  IX 

Chief  Divisions  of  the  Four  Principles — Continued. 

Modes  of  the  Four  Principles 80 

Reflexive  Mode  of  Influence 81 

Methods  of  the  Reflexive  Mode  of  each  Principle 82-1 14 

The  Forms  of  the  Conjunctional  Method 83 

Sexual  I<"orm  of  Selection,  Election,  and  Isolation 83 

Social  Form  of  Selection,  Election,  Isolation,  and  Partition 84 

Filio-parental  Form  of  Selection  and  Election 86 

Forms  of  the  Dominational  Method 86 

Forms  of  the  Impregnational  Method 87 

Dimensional  Form  of  Impregnational  Selection  and  of  Isolation 88 

Structural  Form  of  Impregnational  Selection  and  of  Isolation 88 

Potential  Form  of  Selection  and  Isolation 89 

Fecundal  Selection,  Initial  Fertility,  and  Final  Fertility — Coordina- 
tion is  Secured  by  a  Form  of  Filio-parental  Selection— Some 

Domestic  Fowls  Illustrate  Exaggerated  Initial  Fertility 90^-92 

Fecundal  Selection  in  Human  Races — Loss  of  Fertility  in  the  Poly- 
nesian Race;  not  in  the  African  Race 92 

Statistical  Methods  in  the  Study  of  FertiUty — Karl  Pearson  on  Fer- 
tility in  Man 92-95 

Importance  of  Impregnational  Isolation 95-100 

Segregate  Freedom  from  Competition  and  Segregate  Escape  from 

Enemies loi 

Computation  of  Ratio  of  Cross-breeds  to  Pure-breeds — A  Parallel 

Financial  Problem — Table  from  Formula  (4) 103-106 

Use  of  Tables 107 

Cumulative  Segregation  Resulting  from  Segregative  Endowments.  .  108 

Institutional  and  Prudential  Selection 1 1 1 

Institutional  Election,  Isolation,  and  Partition 114 

Chapter  VII. — Analysis  op  the  Four  Principles  (Continued). 

Methods  and  Forms  of  Environal  Mode  of  Each  Principle 11 5-1 29 

Environal  Selection  and  Election 115 

Environal  Isolation 118 

Industrial   Isolation — Sustentational,   Protectional,   and  Nidifica- 

tional 1 19-1 23 

Chronal  Isolation — Cyclical  and  Seasonal 123-125 

Spatial  Isolation — Geographical  and  Local;  Migrational,  Transpor- 

tational,  and  Geological 125-127 

Fertilizational  Isolation 1 28 

Artificial  Isolation — Importance  of  Environal  Isolation 128 

Environal  Partition 1 29 

Regressive  Mode  of  Each  Principle 1 29-131 

Reversal  of  Partition  and  Isolation  in  Man 1 30 

Isolation  Prevents  Reflexive  Selection  between  Groups 131 

Discriminate  and  Indiscriminate  Action  of  Principles 132-136 

Discriminate  Action , 132 

Indiscriminate  Action 133 

Contrasts  in  Their  Action 134 

Table  of  Discriminate  and  Indiscriminate   Modes    of    the    Four 

Principles 136 


CONTENTS. 


Chapter  VIII. — Classification  op  the  Forms  of  the  Principles  Producing 

Allogamic  Evolution. 

Tables  of  Forms,  with  Brief  Explanations 137-141 

Allogamic,  Autogamic,  and  Agamic  Evolution 137 

Forms  of  the  Four  Principles  of  Segregation 138 

Forms  of  Selection  Defined 139 

Conditions  Determining  Forms  of  Selection 1 40 

Autonomic  and  Heteronomic  Influences 141-144 

Autonomic  Influences  Include  Endonomic  and  Reflexive 141 

Autonomic  Partition  Produces  Autonomic  Isolation 143 

An  Unwarranted  Assumption 144-145 

Chapter  IX. — Summary  and  Conclusion. 

Summary 147-153 

Segregation 147 

Unbalanced  Propagation 148 

Cumulative  Effects  through  Cooperation  of  Difterent  Principles.  ...  150 
Through  the  Operation  of  Same  Principle  in  Successive  Gene- 
rations    1 50 

Amalgamation 151 

Some  of  the  Facts  Emphasized  in  this  Volume •     151 

Conclusion    1 53-158 

What  has  been  Gained  by  Recognition  of  Habitudinal  Segregation  .  153 

Methods  of  Study  that  Should  be  Fully  Applied 153 

Study  of  Organisms  under  Conditions  Favoring  Segregation 154 

Prediction  Confirmed  by  Partula  of  Tahiti 155 

Power  of  Organism  to  Control  its  Relations  to  Environment  In- 
creases with  Stage  of  Evolution  Attained 156 

Chief  Method  of  Advance  is  Tentative  Variation  with  Transmission 

to  Offspring  of  Endowments  of  Survivors 157 

Three  Spheres  of  Progressive  Adjustment — Accommodation,  Co- 
operation, and  Anticipation 158 

Increasing  Recognition  of  Autonomic  Factors 158 

Appendix  I. — A  Small  Portion  of  Divergent  Evolution. 

[From  the  Liniiean  Society's  Journal,  Zoology,  vol.  xx.] 

Reflexive  Segregation 159-174 

Conjunctional  Segregation 159 

Social,  Sexual,  Germinal,  and  Floral  Segregation 160-163 

Impregnational  Segregation 163-171 

Negative  and  Positive  Segregation 163 

Dimensional  and  Structural  Segregation 165 

Potential  Segregation 166-170 

Institutional  Segregation 171 

Concluding  Remarks: 

Impregnational  Segregation  in  EarHer  and  Later  Stages 172 


CONTENTS.  XI 

Concluding  Remarks — Continued. 

Isolation  Usually  Discriminate  and  therefore  Segregative  from  the 

First 174 

Intensive  Segregation  put  in  the  Next  Paper 174 

Table  of  Forms  of  Segregation 176 

Computation  of  Effects  of  Positive  and  Negative  Segregation 177-183 

Table  III 179 

Table  V 1 82 

Appendix  II. — Intensive  Segregation. 

[From  the  Linnean  Society's  Journal,  Zoology,  vol.  xxiil.] 

Classification  of  the  Forms  of  Intensive  Segregation 185-212 

Separation  Always  Involves  More  or  Less  Segregation 186 

Eight  Principles  of  Monotypic  Evolution 187 

Certain  Laws  of  Growth  not  here  Discussed 189 

The  Transformation  of  Freely  Intergenerating  Organisms  never 

Permanently  Divergent 191 

Independent  Transformation  Always  Divergent 191 

Pervasive  Influence  of  Causes  of  Transformation 192 

Utilitarian  and  Non-Utilitarian  Divergence 194 

Selectional  Intension  and  Its  Forms 195-207 

Indiscriminate  Eliminational  Intension 209 

Amalgamational  Intension 211 

Combined  Influence  of  These  Principles 212 

Divergence  of  Mollusks 212-224 

Divergent  Evolution  in  the  Snails  of  Oahu 213-222 

Similar  Facts  Concerning  Land-mollusks  of  Other  Regions 224 

Divergence  in  Insects    225-234 

Divergence  in  Erynnis  and  Thanaos 225 

Divergent  Species  of  Basilarchia 225 

Divergence  in  the  Periodical  Cicada 229 

Concluding  Remarks 234-243 

Outline  of  the  Argument  in  Support  of  Divergence  through  Cumu- 
lative Segregation 234 

Reply  to  Criticism 236 

Construction  of  Permutational  Triangle 241 

Appendix  III. — Letters. 

[Published  in  "  Nature,"  April  10,  May  8,  and  August  14,  1890,  and  April  1,  1897.] 

"Like  to  Like"  a  Fundamental  Principle  in  Bionomics 245-249 

Laws  of  Heredity 249 

Local  Segregation  Often  Initiates  Divergence 247 

Permanent  Difference  in  Innate  Adaptations  not  Necessarily  Ad- 
vantageous Difference 248 

Unstable  Adjustments  as  Affected  by  Isolation 249-252 

Indiscriminate  Separation,  Under  the  Same  Environment,  a  Cause  of 

Divergence 252-2  55 


XU  CONTENTS. 

Indiscriminate  Separation,  etc.,  a  Cause  of  Divergence — Continued. 

Facts  Proving  This 252 

Cessation  of  Reflexive  Selection  Between  Isolated  Sections  Causes 

Divergence  as  Soon  as  Heredity  Weakens 254 

Utility  of  Specific  Characters 255-261 

Right-handedness,  Left-handedness,  and  Similar  Differences 256 

Difference  in  Use  not  Necessarily  Useful  Difference 258 

Divergence  Due  to  Different  Methods  of  Reflexive  Selection  (Jfteu 

Non-advantageous 259 

Different  Methods  of  Using  the  Same  Environment 259 

Letter  by  Mr.  Cockerell,  with  Suggestions  on  the  Facts  Mentioned .  .  260 

Reply  to  Same 261 

Appendix  IV. — List  ok  Papers  on  Evolution,  by  John  T.  Gulick.  262 


EVOLUTION,  RACIAL  AND  HABITUDINAL, 
CONTROLLED  BY  SEGREGATION. 


By  Rev.  John  Thomas  Gulick. 


CHAPTER  I. 

INTRODUCTION. 

I.     Facts  Calling  for  Explanation. 

When  a  number  of  closely  related  varieties  and  species,  occupying 
adjoining  districts  of  very  limited  extent,  come  under  observation, 
the  problems  connected  with  the  origin  of  species  are  liable  to  be 
forced  upon  us.  It  was  therefore  natural  that  when,  in  1851  and 
1852,  I  was  engaged  in  collecting  the  extremely  local  species  of  snails 
found  on  the  island  of  Oahu,  my  mind  was  often  occupied  with  these 
questions.  I  observed  that  each  large  section  of  the  world  had  its 
own  peculiar  forms  of  life,  and  it  seemed  reasonable  to  assume  that 
the  center  of  creation  for  each  form  had,  in  most  cases,  been  within 
the  district  where  it  is  now  found.  The  most  wonderful  limitation  in 
the  areas  of  distribution  for  each  species,  and  accordingly  the  most 
remarkable  localization  of  the  center  of  creation  for  each,  was,  how- 
ever, found  in  the  case  of  the  many  species  of  snails  living  on  the  trees 
of  the  mountain  forests  of  Hawaii.  Bach  valley  seemed  to  be  inhab- 
ited by  peculiar  forms.  Valleys  only  a  mile  apart  were  occupied  by 
distinct  varieties,  and  often  by  different  species.  Groves  of  candle- 
nut  tree  {Aleurites  triloba),  occupying  valleys  5  and  6  miles  apart, 
were  found  to  be  the  homes  of  completely  separate  sets  of  species  of 
snails.  I  had  found  not  simply  a  large  section  of  the  world  within 
which  peculiar  species  had  originated,  but  ascending  a  certain  moun- 
tain ridge  a  few  miles  from  Honolulu,  and  looking  down,  I  could  say, 
"That  valley  to  the  right,  a  couple  of  miles  in  length  and  half  a  mile 
in  width,  is  the  birthplace  of  the  Achatinella  producta  and  Achatinella 
adusta;  and  within  the  groves  of  this  valley  upon  which  we  look  on 
our  left  were  created  A  chatinella  stewartii  and  A  chatinella  johnsonii; 
while  behind  us  a  mile  to  the  northeast,  in  the  jungle  that  clings  to 


2  INTRODUCTION. 

the  almost  precipitous  cliffs  on  the  other  side  of  the  backbone  of  the 
island,  is  the  secret  home  of  the  very  rare  and  beautiful  Achatinella 
versipellis."* 

My  mind  was  constantly  seeking  an  answer  as  to  why  many  of  the 
species  of  these  Hawaiian  genera  of  snails  should  have  an  area  of  distri- 
bution not  more  than  a  mile  or  two  in  length,  while,  in  the  case  of  some 
species  of  terrestrial  mollusks  in  other  parts  of  the  world,  the  district 
occupied  is  a  thousand  miles  or  more  in  length.  Again,  of  Hawaiian 
species,  why  should  those  living  continuously  in  the  trees,  without 
descending  to  the  ground  even  for  breeding,  occupy  on  the  average 
areas  much  smaller  than  those  occupied  by  species  living  contin- 
uously on  the  ground? 

The  mystery  was  only  intensified  when  I  observed  a  certain  corre- 
lation between  the  form  of  the  island  on  which  the  species  had  origi- 
nated and  the  method  of  grouping  and  distribution  of  the  species  and 
varieties.  In  the  first  place,  the  forest  species  on  one  island  are  never 
completely  intergraded  with  those  on  another  island.  Again,  the 
intergrading  of  nearly  allied  species  on  one  island  usually  relates  to 
species  found  in  contiguous  valleys ;  while  the  most  divergent  forms 
are  found  in  the  districts  that  are  most  widely  separated.  On  West 
Maui,  which  is  a  single  conical  mountain,  deeply  furrowed  with  val- 
leys and  gorges  radiating  from  one  center,  we  find  each  group  of 
species  lying  in  a  circle  around  the  mountain,  each  species  occupying 
its  own  district,  though  intergrading  with  those  of  adjoining  districts, 
and  no  one  of  the  species  strongly  divergent  from  any  of  the  others 
of  the  same  group — a  distribution  that  seemed  symmetrical  and 
impressed  me  as  strikingly  similar  to  the  distribution  of  groups  of 
birds  and  mammals  around  the  North  Pole ;  for  example,  the  distribu- 
tion of  species  of  bears  throughout  the  Northern  Hemisphere.  But, 
in  strong  contrast  with  this,  is  the  distribution  of  species  of  snails  on 
the  island  of  Oahu.  Here  the  forest  region,  in  which'  the  snails  are 
mostly  found,  is  not  spread  in  a  circular  form  over  a  group  of  radiat- 
ing valleys,  but  lies  in  a  strip  about  35  miles  in  length  and  from  2  to 
6  miles  in  width,  upon  a  mountain  range;  and  the  forms  of  one 
closely  related  group  are  distributed  in  two  parallel  series  of  species 
on  opposite  sides  of  the  ridge,  the  most  divergent  forms  being  those 

*  In  Plate  II,  figs.  1 1-25,  are  given  15  species  of  Achatinella,  distributed  in  the 
groves  of  five  valleys,  and,  therefore,  limited  to  an  area  less  than  5  miles  in 
length  and  not  more  than  2  miles  in  width.  Of  these  15  species  there  are  nearly 
a  hundred  easily  distinguished  varieties.  Moreover,  several  other  much  rarer 
forms  of  Achatinella  found  on  the  vegetation  of  the  same  district  have  been  de- 
scribed as  separate  species;  and  of  6  other  genera  of  the  family  Achatinellidae 
there  are,  within  the  same  limits,  17  or  18  strongly  marked  species. 


.  SELECTION  NOT  ALWAYS  THE  CAUSE.  3 

that  are  separated  by  the  greatest  distance,  which  also  corresponds 
with  separation  by  the  greatest  number  of  valleys  and  mountain 
spurs. 

I  had  read  Darwin's  account  of  the  Galapagos  Islands  given  in 
"The  Voyage  of  the  Beagle,"  and  had  noted  the  astonishment  with 
which  he  had  discovered  that  islands  within  sight  of  each  other  were 
the  homes  of  closely  related  but  diverse  species — a  marvel  which 
he  in  no  way  attempted  to  explain;  and  here,  in  the  snails  of 
Hawaii,  I  had  found  differences  more  wonderful,  for  each  valley  of 
the  same  island  was  the  home  of  peculiar  forms.  When  Darwin's 
"Origin  of  Species"  appeared  in  1859  I  read  it  with  intense  interest 
and  with  complete  assent  to  his  argument  that  large  groups  of  widely 
divergent  species  had  been  derived  from  common  ancestry ;  but  the 
moi-e  I  meditated  on  the  scope  of  natural  and  sexual  selection  as  fac- 
tors producing  transformation,  the  more  clearly  I  perceived  that  they 
were  not  adequate  to  explain  the  diversity  of  these  species  exposed  to 
the  same  external  conditions;  neither  did  they  afford  any  explana- 
tion of  why  the  areas  of  distribution  for  many  of  these  species  are  so 
extremely  limited,  while  some  species  of  terrestrial  mollusks  are  dis- 
tributed over  vast  areas. 

II.  Facts  showing  that  in  the  case  op  many  Divergent  Species  Diversity 
OF  Natural  and  Sexual  Selection  is  either  Wanting  or,  if  Present, 
IS  THE  Effect  and  not  the  Cause  of  the  Divergence.* 

1 .  In  Many  Cases  of  Divergence  Diversity  of  Sexual  Selection  can  not 
be  the  Cause. 

In  the  case  of  mollusks,  the  diversity  in  colors  and  forms  presented 
by  closely  allied  varieties  and  species  can  not  be  attributed  to  diver- 
sity in  the  direct  action  of  the  sexual  instincts  of  the  different  groups, 
by  wrhich  those  of  certain  forms  and  colors  are  allowed  to  mate,  to  the 
exclusion  of  all  other  forms  and  colors;  for  there  is  no  reason  to 
believe  that  differences  of  form  and  color  are  capable  of  being  at  all 
observed  by  the  senses  with  which  they  are  endowed.  Even  in  the 
case  of  highly  endowed  animals,  vv^here  diversity  in  the  styles  of  orna- 
mentation desired  in  mates,  and  therefore  diversity  in  the  forms  of 
sexual  selection  in  closely  allied  varieties  and  species,  may  be  readily 
granted,  the  problem  of  chief  interest  is  not  concerning  the  effect  of 
these  divergent  instincts,  but  rather  concerning  the  causes  by  which 
they  have  been  produced;  for  why  should  an  isolated  section  of  a 
species  possess  instincts  in  any  degree  differing  from  the  instincts  of 
the  main  body  of  the  species?     Sexual  selection  is,  therefore,  an  in- 

*  In  Chapter  IV  will  be  found  illustrations  of  divergence  under  the  same  envi- 
ronment. 


4  INTRODUCTION. 

complete  explanation  of  divergence,  even  for  higher  animals ;  and  in 
the  case  of  creatures  as  low  as  moUusks  it  would  seem  to  be  entirely- 
excluded  from  having  any  effect  in  determining  the  diversity  of  color 
in  the  different  species. 

2.  In  Many  of  the  Same  Cases  Diversity  of  Natural  Selection  can  not 
be  the  Cause. 

First.  Because  in  many  cases  divergence  is  not  in  proportion  to  the 
degree  of  difference  in  the  environments  surrounding  the  separated  varie- 
ties and  species.  This  is  true  not  only  in  regard  to  the  divergence  of 
genera  and  subgenera  of  snails,  occupying  different  islands  of  the 
Hawaiian  group,  but  in  regard  to  the  divergence  of  the  varieties  and 
species  of  the  same  subgenus,  occupying  the  different  districts  of 
the  same  island.  Darwin's  theory  assumes  that  when  a  few  members 
of  a  species  form  a  colony  in  a  new  district  divergence  is  produced 
only  when,  and  in  proportion  as,  the  new  district  presents  condi- 
tions unlike  those  found  in  the  original  habitat  of  the  species.  This 
interpretation  fails  to  explain  the  origin  of  the  species  we  are  now 
considering.  For  example,  valleys  separated  by  narrow  mountain 
spurs,  on  the  southwest  side  of  the  main  mountain  range  of  the  island 
of  Oahu,  are  exposed  to  similar  wind,  rain,  and  temperature ;  the  soil 
has  come  from  the  disintegration  of  volcanic  rock,  without  limestone ; 
the  vegetation  on  the  ridges  differs  from  that  in  the  valleys;  but  in 
most  of  the  valleys  we  find  groves  of  candlenut  trees  (Aleurites  tri- 
loba), and  clinging  to  the  trunks  and  branches  of  the  trees  in  these 
groves  in  any  one  valley  we  find  several  species  and  many  varieties 
that  are  not  exactly  reproduced  in  any  valley  more  than  2  or  3  miles 
distant.  The  valleys  of  Manoa  and  Nuuanu  are  but  3  miles  apart, 
but  they  present  a  greater  difference  in  vegetation  than  that  found 
between  Manoa  and  Kawailoa,  which  are  20  miles  apart ;  the  diver- 
gence in  species  of  Achatinella  occupying  these  valleys  is,  however, 
much  less  in  the  former  case  than  in  the  latter.  This  is  the  reverse 
of  what  we  should  find  if  the  divergence  were  due  to  exposure  to  unlike 
conditions.  This  is  not  an  exceptional  case.  The  land  mollusks  of 
the  Hawaiian  Islands  present  a  vast  body  of  facts  of  this  kind. 

Second.  Because  in  some  cases  the  divergence  is  in  non-utilitarian 
characters.  If  these  snails  were  endowed  with  powers  of  vision  and 
discriminating  instincts  as  highly  developed  as  those  of  birds,  it 
might  be  argued  that  the  brilliant  colors  characterizing  certain 
species  were  developed  by  what  I  have  called  social  segregation,  with 
the  aid  of  sexual  and  social  selection,  including  the  need  of  recognition 
marks,  which  Mr.  Wallace  has  pointed  out  as  a  prime  necessity  in  the 
segregation  of  higher  animals;  but,  as  we  have  no  reason  to  think 


SELECTION  NOT  ALWAYS  THE  CAUSE.  5 

that  they  possess  the  power  of  discriminating  colors,  we  must  seek 
some  other  explanation.  If  the  colors  were  of  a  protective  character 
we  might  surmise  that  they  had  been  developed  through  exposure 
for  many  generations  to  sharp-sighted  enemies;  but  in  the  case  of 
many  of  the  species,  their  white  and  green  tints  striped  with  black 
make  them  conspicuous  objects  against  the  brown  trunks  of  the  trees 
on  which  they  are  constantly  found.  Neither  are  their  colors  for 
warning;  for  these  snails  are  not  repulsive  to  flesh-eating  birds.  It 
is,  therefore,  hard  to  avoid  the  thought  that  these  striking  colors  are 
of  no  service  in  protecting  the  life,  either  of  the  individual  or  of  the 
species.  Again,  certain  birds  of  prey  are  the  only  aboriginal  crea- 
tures that  could  be  suspected  of  feeding  on  these  snails;  and  as  the 
birds  have  a  wide  range,  the  immense  diversity  of  color  in  the  snail 
shells  of  one  island  would  remain  unexplained. 

There  is,  also,  another  character  in  which  species  of  some  of  these 
genera  often  differ  from  each  other,  in  regard  to  which  natural  selec- 
tion has  never  been  shown  to  be  the  controlling  factor.  I  refer  to  the 
character  of  the  coil  of  the  shell,  which  may  be  dextral  in  one  species, 
sinistral  in  another,  and  either  dextral  or  sinistral  in  a  third.  As  long 
as  it  is  impossible  to  give  any  reason  why  a  species  would  not  be 
equally  successful  if  every  individual  possessed  the  reverse  form  from 
that  it  now  has,  it  is  unreasonable  that  we  should  attribute  the  pres- 
ent form  to  the  influence  of  natural  selection. 

The  theory  that  there  is  great  advantage  for  the  species  in  having 
all  the  individuals  coiled  in  the  same  way,  if  proved,  would  in  no  way 
explain  why  certain  species  are  always  dextral  and  certain  others  are 
always  sinistral,  while  some  well-established  species  present  large 
masses  of  individuals  of  each  form.  I  think  it  will  some  day  be 
shown  that  snails  of  opposite  forms,  though  of  the  same  race,  are  in- 
capable of  mating  with  each  other,  and  we  already  know  that  each 
individual  is  both  male  and  female.  If,  then,  an  unusual  sport  should 
produce,  in  the  same  family,  or  on  the  same  tree,  two  individuals  of 
the  reverse  form  from  their  parents,  we  should  have  a  completely 
segregated  variety  established  in  the  original  home,  while  exposed  to 
the  same  environment  and  using  it  in  the  same  way,  and  its  new  char- 
acter conferring  no  benefit. 

Third.  Because  in  the  case  of  certain  divergent  species  of  Achatinella, 
occupying  isolated  valleys  presenting  the  same  vegetation,  the  diversity  of 
selection  to  which  they  are  subjected  through  different  habits  of  feeding  is 
directly  preserved  by  the  isolation  which  prevents  the  peculiar  habits  from 
being  broken  down  by  free  crossing.  The  habits  of  feeding  are  not  with- 
out variation  even  in  the  original  valley.     When,  therefore,  one  or  two 


6  INTRODUCTION. 

individuals  with  a  special  habit  of  feeding  are  transported  to  a  new 
valley,  it  is  not  at  all  strange  that  they  choose  to  pass  by  some  plants 
used  by  many  varieties  of  the  species  in  the  original  home.  More- 
over, their  descendants  may  never  regain  the  power  to  feed  on  as  many 
kinds  of  plants;  or,  if  on  as  many,  probably  not  on  the  same  kinds. 
Still  further,  when  a  distant  valley  has  been  reached,  after  a  number 
of  such  transfers,  each  transfer  being  followed  by  a  long  history  of 
habit  building,  without  the  influence  of  crossing  with  individuals  of 
the  original  stock,  is  it  at  all  strange  that  the  habits  have  become 
widely  divergent,  and  that  they  are  the  cause  of  divergent  selection 
tending  to  establish  the  divergent  habits  in  a  more  fixed  form  ? 

In  such  a  case  as  the  one  just  described  the  new  habit  and  the 
diversity  of  selection,  with  the  diversity  in  the  direct  influence  of  the 
environment,  can  not  be  ascribed  to  any  advantage  over  the  old  form 
resulting  from  the  new  habit ;  for  competition  with  the  old  form  has 
ceased  for  countless  generations.  Moreover,  if  the  later  history  of 
the  newer  species  has  been  in  a  new  and  unoccupied  district,  compe- 
tition with  all  allied  forms  has  ceased;  and  the  new  habit  is  simply 
one  of  several  forms  of  using  the  environment  that  are  open  to  a  new 
colony,  unaffected  by  constant  crossing  with  the  old  stock. 

III.     May  not  the  Prevention  of  Free  Crossing  be  an  Explanation? 

It  will  probably  have  already  occurred  to  many  of  my  readers  that 
the  wonderful  limitation  in  the  areas  of  distribution  occupied  by  the 
separate  species  of  Hawaiian  snails  is  in  some  way  connected  with 
lack  of  powers  and  opportunities  for  migration ;  and  now  as  we  reflect 
that  the  same  lack  of  migration  would  immeasurably  increase  the 
isolating  effect  of  some  rare  occurrence  by  which  a  single  individual 
is  carried  a  mile  or  two  beyond  the  home  of  the  species,  into  a  region 
of  abundant  food,  the  question  naturally  arises  whether  the  isolation, 
which  prevents  all  chance  of  crossing  with  the  original  stock,  does  not 
open  the  way  for  new  habits,  for  new  forms  of  selection,  and  accord- 
ingly for  the  transformation  of  the  new  colony  into  a  new  variety, 
and  finally  into  a  new  species. 

We  have  here  reached  the  idea  of  freedom  from  crossing  with  the 
old  stock,  or  isolation,  in  the  broader  meaning  which  has  been  given 
to  the  term  by  writers  on  evolution  since  the  days  of  Darwin.  I  be- 
lieve that  no  process  of  natural  selection,  or  of  sexual  selection,  or  of 
any  other  form  of  selection,  can  transform  one  species  into  two  or 
more  species  without  the  prevention  of  free  crossing  between  the 
branches  that  are  thus  transformed.     Isolation  is,  I  believe,  an  essen- 


CAUSES  AND  ElflfECTS  Olf  SEGREGATION.  7 

tial  factor  in  the  production  and  maintenance  of  divergent  types, 
whether  they  be  varieties  or  species;  and  any  theory  that  fails  to 
consider  the  causes  and  effects  of  isolation  is  an  insufficient  explana- 
tion of  divergent  evolution.  Still  further,  as  the  general  trend  of  all 
evolution  is  toward  increasing  divergence,  the  influence  of  isolation 
is  fundamental  in  all  the  processes  of  organic  evolution. 

IV.    Investigation  of  the  Causes  and  Effects  op  Segregation. 

The  purpose  of  this  volume  is  to  investigate  the  causes  and  effects 
of  what  I  have  called  "segregate  breeding,"  or  simply  "segregation." 
Segregation  is  the  intergeneration  of  like  with  like,  with  the  preven- 
tion of  crossing  between  unhke  groups.  I  maintain  that  segregation 
ranks  as  one  of  the  fundamental  principles  controlling  the  relations 
of  organic  beings  to  each  other.  Moreover,  in  the  processes  of  organic 
evolution,  the  principles  controlling  the  modification  of  segregation 
are  the  principles  that  control  the  variation  and  heredity.  It  is  only 
as  it  aids  in  producing  and  intensifying  segregation  that  any  form  of 
selection  becomes  effective  in  the  evolution  of  organic  types.  I 
maintain  that  the  inheritance  of  acquired  characters  is  not  yet  fully 
proved  or  disproved;  but  if  future  investigation  should  show  that 
the  special  training  of  parents  for  several  generations  results  in  the 
transmission  to  offspring  of  modified  innate  endowments,  there  could 
be  no  doubt  that  to  gain  the  full  effect  of  such  training  on  offspring 
there  must  not  be  free  crossing  between  the  trained  and  the  untrained. 
Segregation,  even  under  such  conditions,  remains  a  leading  factor, 
and  modification  of  segregation  will,  I  believe,  be  found  to  be  the 
principle  controlling  the  evolution. 

Lamarck  recognized  that  distinct  organic  types  could  not  be  main- 
tained without  some  form  of  isolation  ;*  and  such  Neo-Iyamarckians 
as  Professor  Packard  have  been  even  more  emphatic  in  placing  this 
principle  among  the  essential  conditions  for  divergent  evolution. f 

V.    Segregation  the  Unifying  Principle  in  the  Complex  Process  of 

Evolution. 

If  heredity  is  a  fundamental  power,  then  segregate  breeding  must 
be  a  fundamental  principle  in  the  formation,  continuance,  and  control 
of  divergent  types;  for  diversity  of  type  is  diversity  of  inheritance, 
and  diversity  of  inheritance  can  not  be  initiated  or  maintained  where 

*  "Lamarck,  His  Life  and  Work,"  by  A.  S.  Packard.     New  York  and  London. 
Longmans,  Green  &  Co.     pp.  319,  320. 
t  Ibid.,  pp.  392-396  and  404-406. 


8  INTRODUCTION. 

there  is  a  free  blending  of  the  different  types  of  inheritance.  Now,  it 
is  recognized  by  all  that  the  influence  of  the  different  forms  of  selec- 
tion rests  on  heredity;  if,  therefore,  we  so  expound  natural  selection 
as  to  deny  the  fundamental  laws  of  heredity  expressed  in  the  depend- 
ence of  divergence  on  segregate  breeding,  we  undermine  the  founda- 
tions on  which  the  importance  of  selection  rests.  Clear  recognition 
of  the  laws  of  life  makes  it  plain  that  a  consistent  theory  of  divergent 
evolution  can  not  be  constructed  without  considering  the  principles 
by  which  segregate  breeding  is  modified  and  intensified.  Those  who 
trace  these  principles,  and  who  show  that  diversity  of  natural  selec- 
tion and  the  other  forms  of  selection  are  effective  in  producing  diver- 
gent types  only  when  cooperating  with  isolation  in  producing  segre- 
gate breeding,  are  simply  recognizing  the  unfailing  influence  of  hered- 
ity. Segregation  is  the  fundamental  process  to  which  all  the  princi- 
ples helping  to  produce  divergent  evolution  must  contribute. 

I  consider  it  important  to  recognize  the  very  different  spheres 
filled  by  the  principles  of  selection  and  isolation,  and  to  so  define  the 
terms  that  they  do  not  overlap.  But  I  also  maintain  that  there  is  a 
correlation  in  the  two  processes,  in  that  both  cooperate  in  controlling 
heredity  and  variation,  and  so  in  producing  ever-increasing  segregation 
of  organic  types.  The  fundamental  unity  of  the  processes  producing 
evolution,  whether  these  processes  are  originated  and  controlled  by 
innate  powers  or  by  acquired  characters,  and  whether  these  powers 
maintain  relations  with  other  members  of  the  species  or  with  condi- 
tions external  to  the  species,  is  found  in  the  fact  that  they  all  co- 
operate in  producing  segregation. 


CHAPTER  II. 

BIONOMIC  LAWS. 

I.     BiONOMic  Laws  and  the  Method  of  their  Investigation. 
1 .  Bionomics  and  Its  Scope. 

The  organic  world  as  we  find  it  consists  of  many  groups  of  individ- 
uals, each  group,  with  but  few  exceptions,  being  propagated  by  the 
union  of  male  and  female  elements  produced  by  parents  belonging  to 
the  same  group;*  while  the  elements  of  different  groups  are  either 
incapable  of  fruitful  union  or  in  nature  seldom  have  an  opportunity 
for  such  union.  Each  group  possesses  characters  of  its  own,  distin- 
guishing it  from  all  other  groups;  and  these  characters  are  inherited 
by  each  successive  generation  of  the  group,  except  in  cases  known  as 
alternating  generations,  in  which  the  persistence  of  character  is  re- 
vealed in  a  series  of  two  or  more  generations  that  return  to  the 
original  form.  These  persistent  groups  which  are  prevented  from 
crossing  by  the  incompatibility  of  their  sexual  elements  or  by  some 
other  form  of  segregation  are  usually  called  species;  but  when  the 
difference  of  character  is  slight  they  are  often  called  varieties;  and 
when  the  differences  are  not  easily  recognized  they  are  not  even 
regarded  as  different  varieties.  Each  persistent  group  differing  more 
or  less  from  every  other  group,  and  reproducing  its  own  form  without 
commingling  with  other  forms,  I  call  a  type. 

The  doctrine  of  evolution  teaches  that  the  vast  multitude  of  organic 
types  now  inhabiting  the  world  are  the  descendants  of  but  few  and 
perhaps  of  but  one  original  type.  Bionomics  is  the  science  that  treats 
of  the  origin  of  organic  types  and  of  the  relations  in  which  they  stand 
to  each  other  and  to  the  physical  environment,  f  In  this  volume  some 
of  the  fundamental  laws  of  bionomics  will  be  considered. 

2.  Why  we  Commence  with  the  Method  of  Evolution  without  first  proving 
the  Fact  of  Evolution. 

It  may  be  thought  by  some  of  my  readers  that  before  discussing  the 
laws  of  evolution  logical  method  would  demand  that  I  should  consider 

*  Examples  of  these  exceptions  are  found  in  plants  that  propagate  by  shoots  or 
bulbs  without  ever  producing  seed,  such  as  banana;  also  in  parthenogenetic 
plants  and  animals. 

t  Prof.  E.  Ray  Lankester  has  proposed  this  use  of  the  word  "bionogiics"  in  the 
article  on  Zoology,  in  Encyc.  Brit.,  9th  ed. 

9 


lO  BIONOMIC  I.AWS. 

whether  the  evolution  of  species  is  anything  more  than  a  doubtful 
hypothesis.  In  other  words,  it  may  be  thought  that  the  attempt  to 
explain  the  method  of  evolution  before  it  has  been  proved  that  there 
is  such  a  process  is  an  inversion  of  logical  method.  Further  consid- 
eration will,  however,  show  that  the  greatest  obstacle  to  the  general 
acceptance  of  the  theory  of  evolution  has  been  the  difficulty  in  believ- 
ing that  this  wonderful  transformation  is  being  wrought  out  in  our 
very  presence,  and  that  the  laws  in  accordance  with  which  it  pro- 
gresses are  in  a  large  degree  open  to  investigation. 

The  possibility  of  recognizing  this  stupendous  reality  has  been  shut 
out  of  the  mind  by  the  double  assumption  that  the  methods  of  crea- 
tion are  necessarily  inscrutable  and  that  the  process  of  creation  has 
been  closed  never  to  be  reopened.  As  both  these  assumptions  are 
without  proof,  the  shortest  method  of  setting  them  aside  is  to  show 
that  the  energies  of  creation  are  ever  working  in  the  ordinary  pro- 
cesses of  life.  The  effectiveness  of  this  general  method  of  appeal  to 
actual  experience  and  observation  is  seen  in  Darwin's  "Origin  of 
Species."  He  there  first  shows  that  a  process  of  breeding,  which  in 
domestication  always  results  in  divergent  varieties,  is  also  being  car- 
ried on  by  natural  causes.  He  then  shows  that  if  we  assume  that 
species  have  been  produced,  one  from  another,  by  some  such  process, 
the  relations  of  species  to  species,  not  only  in  the  groups  of  scientific 
classification,  but  also  in  their  geographical  distribution  over  the 
earth  and  in  their  geological  successions  in  time,  become  intelligible, 
and  present  a  network  of  interrelated  and  significant  phenomena,  the 
causes  of  which  can  be  more  or  less  fully  traced.  I  propose  to  follow 
the  same  general  method.  But  as  present  debate  relates  to  the  prin- 
ciples and  causes  on  which  evolution  depends  rather  than  to  the  proof 
that  such  evolution  has  taken  place,  I  shall  give  my  chief  attention 
to  the  first  part  of  the  argument.  I  shall  discuss  the  forms  and  laws 
of  bionomic  action  by  which  the  relations  of  species  to  species  are 
being  maintained  or  modified,  and  shall  refer  to  the  results  of  this 
action  as  revealing  the  nature  of  the  process. 

3.  Need  of  Investigation  of  all  the  Forms  of  Interaction  causing 
Transformation. 

Inquiries  leading  to  the  discovery  of  bionomic  laws  have  usually 
been  first  suggested  by  observing  the  relations  under  which  organ- 
isms present  themselves  as  distributed  in  nature ;  but  after  we  have 
once  recognized  the  fact  that  these  relations  are  the  result  of  the 
constant  interaction  between  organism  and  organism,  and  between 
the  organism  and  the  physical  environment,  it  becomes  necessary  to 


THE  METHOD  OF  THEIR  INVESTIGATION.  1 1 

make  a  full  classification  of  the  different  forms  of  interaction  that 
tend  to  modify  the  species.  A  systematic  and  thorough  use  of  this 
method  will,  I  am  convinced,  throw  light  on  many  problems,  correcting 
many  partial  and  incomplete  theories.  We  may  also  hope  that  a 
careful  examination  of  the  different  forms  of  interaction  will,  in  some 
degree,  lessen  the  danger  of  attributing  exclusively  to  one  form  of 
interaction  results  that  are  really  due  to  several  forms.  And  having 
discovered  that  similar  results  are  produced  by  different  forms  of 
action,  we  are  next  led  to  seek  for  the  underlying  principle  in  which 
they  agree. 

4.  Natural  and  Sexual  Selection  not  the  only  Factors  producing 
Transformation. 

The  relation  of  the  species  found  in  any  one  of  the  Galapagos 
Islands  to  those  found  on  other  islands  of  the  same  archipelago,  and, 
still  further,  their  relation  to  the  species  in  South  America,  suggested 
to  Darwin  the  idea  that  they  had  arisen  through  the  modification  of 
South  American  species.  This  idea  he  elaborated,  supplementing 
and  supporting  it  by  attributing  the  transformation  of  species  to  two 
chief  causes — natural  and  sexual  selection.  That  these  two  factors 
must  be  effective  in  producing  permanent  transformation  was  argued 
from  the  effect  of  artificial  selection  in  producing  divergent  races  of 
domestic  plants  and  animals,  and  from  the  observed  fact  that  in 
many  cases  natural  varieties  and  species  present  degrees  of  diver- 
gence corresponding  to  the  time  during  which  they  must  have  been 
exposed  to  different  environments.  These  principles  have  thrown  a 
flood  of  light  on  differences  between  the  sexes  of  the  same  species,  and 
on  those  differences  of  species  by  which  they  are  adapted  to  their 
different  environments;  but  do  they  show  that  there  can  be  no 
divergence  in  the  isolated  portions  of  a  species  exposed  to  the  same 
environment,  or  that  all  the  divergences  that  arise  in  portions  ex- 
posed to  different  environments  are  adaptations  to  the  environment? 
Are  all  the  diversities  of  sexual  selection  by  which  different  portions 
of  a  species  are  differently  modified  due  to  differences  in  the  environ- 
ments of  these  portions?  If  not,  we  have  a  cause  of  divergence  that 
does  not  depend  on  exposure  to  different  environments.  Moreover, 
if  we  assume,  as  most  do,  that  the  differences  in  sexual  selection  in  the 
separate  portions  of  a  species  are  due  to  differences  in  the  sexual 
instincts  of  the  portions,  the  question  arises  as  to  how  we  are  to 
explain  the  divergence  in  the  sexual  instincts  of  individuals  exposed 
to  the  same  environment.  Is  it  not  apparent  that  in  the  facts 
brought  forward  for  the  proof  of  this  principle  of  transformation  other 
principles  are  involved? 


12  BIONOMIC  LAWS. 

Further  observation  brings  to  light  many  cases  in  which  separated 
portions  of  a  species  have  adopted  different  industrial  habits,  while 
exposed  to  the  same  set  of  conditions,  the  diversity  in  the  forms  of 
selection  by  which  they  are  molded  being  due  to  the  different  uses 
they  have  made  of  the  same  resources,  and  not  to  any  difference  in 
the  resources  found  in  the  different  districts. 

As  these  facts  will  be  presented  in  detail  when  discussing  the  prin- 
ciples upon  which  I  believe  they  depend,  I  need  not  dwell  upon  them 
here.  It  is  sufficient  for  our  present  purpose  to  show  that  the  prob- 
lems of  divergence  are  not  fully  explained  by  natural  and  sexual 
selection. 

5.  Comparison  of  the  Conditions  to  which  Natural  Species  are  Exposed 
with  the  Conditions  producing  Domestic  Varieties. 

Believing  that  other  principles  besides  natural  and  sexual  selection 
must  be  effective  in  the  production  of  specific  differences,  I  propose  to 
make  systematic  search  for  them  in  the  interactions  between  the 
members  of  the  same  species  and  between  the  species  and  the  environ- 
ment. Following  the  example  of  Darwin  and  Wallace,  I  shall  seek 
suggestions  for  the  guidance  of  my  search  from  the  experience  of  the 
breeder  of  artificial  races.  In  the  maxims  and  traditions  of  those 
who  are  engaged  in  raising  highly  prized  varieties  of  plants  and  ani- 
mals, we  have  the  treasured  results  of  thousands  of  years  of  experi- 
ment in  biology.  In  these  results  we  shall,  I  think,  find  principles 
that  have  not  been  fully  considered  in  the  problems  of  evolution. 
This  method  of  presenting  the  subject  I  adopt  as  best  suited  for 
exhibiting  the  relations  in  which  the  different  laws  stand  to  each 
other,  but  I  would  not  wish  to  have  anyone  suppose  that  it  represents 
the  order  of  the  steps  by  which  these  laws  were  first  reached  and  by 
which  their  relations  to  the  origin  and  transformation  of  species  were 
first  recognized.  The  problems  requiring  solution  were  in  every  case 
forced  upon  my  attention,  not  by  the  study  of  domestic  races,  but  by 
observing  the  conditions  under  which  divergence  has  arisen  between 
natural  varieties  and  species.  Having  discovered  that  in  nature 
many  divergencies  appear  in  varieties  and  closely  allied  species  ex- 
posed to  the  same  environment,  and  sometimes  in  those  using  the 
environment  in  the  same  way,  I  concluded  that  natural  selection 
could  not  be  the  essential  and  fundamental  factor  in  the  multiplica- 
tion of  species.  I  then  turned  to  the  production  of  domestic  races, 
and  found,  on  the  one  hand,  that  artificial  selection  could  avail  noth- 
ing in  producing  divergent  forms,  unless  it  was  aided  by  isolation, 
and,  on  the  other  hand,  that  isolation,  if  not  producing  divergence 


THE  PRODUCTION  Oif  DOMESTIC  RACES.  1 3 

from  the  first,  was  sure,  when  long  continued,  to  end  in  divergence, 
either  through  diversity  in  the  habits  determining  the  use  of  resources 
or  through  some  other  principle  producing  transformation  of  the 
isolated  portion  of  the  species.  These  conclusions,  gathered  from 
the  experience  of  the  breeder,  were  then  applied  to  the  explanation 
of  the  phenomena  of  divergence  as  appearing  in  nature,  and  any 
residual  phenomena  not  at  first  explained  were  again  brought  to  the 
test  of  experiment  as  revealed  in  the  experience  of  the  breeder.  The 
process  of  discovery  is  often  very  intricate,  while  that  of  exposition 
and  proof  is  comparatively  simple  and  direct ;  and  it  is  not  surprising 
that  this  has  been  found  to  be  especially  true  in  the  case  of  the  laws 
governing  the  complex  relations  determining  the  evolution  of  species. 

II.    The  Production  of  Domestic  Races. 

Six  subjects  must  be  considered.  In  studying  the  production  of 
domestic  races  we  need  to  take  up  separately  the  different  results 
reached,  with  the  methods  by  which  each  result  is  realized,  and  the 
conditions  that  are  necessary  for  success.  We  shall  consider :  (i)  the 
conditions  on  which  the  continuance  of  the  race  or  species  depends ; 
(2)  the  process  by  which  a  race  possessing  certain  characters  is  trans- 
formed into  a  race  possessing  different  characters;  (3)  the  process 
by  which  one  race  is  transformed  into  several  races;  (4)  the  pro- 
cess by  which  the  stability  of  a  new  breed  is  established;  (5)  the 
process  by  which  divergent  races  are  amalgamated  and  commingled ; 
and  (6)  the  influence  of  acquired  characters  on  racial  characters. 

1 .  The  Continuance  of  Races. 

In  the  domestication  of  any  species  one  of  the  first  questions  is, 
Can  food  or  other  needed  resources  for  maintaining  its  life  be  fur- 
nished under  domestication;  and  if  so,  has  it  adaptations  to  the 
wants  of  man  such  as  to  induce  him  to  furnish  the  needed  mainte- 
nance? If  this  double  question  can  be  answered  in  the  affirmative, 
the  probability  of  its  being  domesticated  will  turn  on  its  retaining  its 
power  of  propagating  when  brought  under  the  new  conditions.  The 
elephant,  though  a  useful  animal,  has  failed  of  developing  a  domestic 
race  through  failing  to  propagate  with  any  certainty  under  domesti- 
cation. The  preservation  of  a  domestic  race  depends  on  its  securing 
maintenance  through  adaptation  to  the  rational  environment,  just  as 
the  propagation  of  a  species  under  nature  depends  on  its  securing 
maintenance  through  adaptation  to  the  natural  environment;  and  if 
either  the  race  or  the  species  is  to  survive  there  must  be  such  co- 


14  BIONOMIC  LAWS. 

ordination  between  sex  and  sex,  and  between  the  sexual  elements  of 
the  group,  as  will  secure  impregnation,  and  the  production  of  both 
male  and  female  elements  must  be  sufficient  to  prevent  extinction. 

2.   The  Transformation  of  Races. 

The  survival  of  a  race  or  species  depends  on  its  having  sufficient 
adaptation  to  the  environment  to  secure  maintenance,  on  there  being 
sufficient  compatibility  between  the  sexes  to  secure  fertility,  and  on 
the  production  of  male  and  female  elements  in  sufficient  abundance 
to  secure  fecundity;  but  the  presence  of  these  conditions  does  not 
insure  the  transformation  of  the  race  or  species  enjoying  these  condi- 
tions, nor  does  the  extinction  of  races  or  species  lacking  in  these  con- 
ditions insure  transformation  in  the  surviving  forms.  As  domestica- 
tion prevents  or  greatly  impairs  reproduction  in  the  elephant,  this 
species  does  not  survive  under  domestication  and  therefore  escapes 
the  transformation  necessary  to  produce  a  domestic  race.  For  a 
similar  reason,  the  complete  extermination  of  the  American  bison 
would  not  produce  a  new  race  of  bisons ;  and  it  could  have  influence 
in  transforming  an  associated  species  of  some  other  family  only  in 
case  the  absence  of  the  bison  should  introduce  a  change  in  the  relative 
degrees  of  maintenance,  compatibility,  or  fecundity  possessed  by  the 
different  variations  of  the  species,  so  that  the  most  successful  should 
be  other  than  those  that  were  most  successful  during  the  period  of 
association  with  the  bison.  A  little  reflection  will  reveal  the  fact 
that  when  the  change  of  relative  degrees  of  maintenance  or  fecundity 
pertains  to  races  or  species  which  are  entirely  prevented  from  crossing 
the  relative  numbers  in  which  these  groups  exist  will  be  changed,  but 
that  this  will  not  be  a  cause  of  change  in  the  characteristics  of  the 
groups,  even  if  some  of  them  become  extinct.  This  will  be  distinctly 
seen  if  we  take  a  definite  case.  For  example,  during  one  year  turkeys 
may  attract  the  attention  of  a  poulterer,  and  the  next  year  peafowls 
may  become  his  favorites ;  but  the  change  in  the  relative  importance 
given  to  either  species  transforms  neither  the  one  or  the  other. 
Again,  he  may  have  a  pair  of  a  species  which  he  would  gladly  multi- 
ply, but  through  difficulty  in  getting  them  to  mate  his  success  may  be 
very  limited ;  or  in  the  case  of  a  second  desirable  species  that  pairs 
freely,  diminished  fecundity  may  interfere  with  their  multiplication, 
while  at  the  same  time  a  third  species  of  no  great  value,  but  not 
limited  by  these  disabilities,  multiplies  freely  and  is  raised  in  large 
numbers.  The  point  to  be  observed  is  that  in  all  these  cases  the 
difference  in  the  degrees  of  propagation  of  these  different  species  is 
not  a  cause  of  transformation  in  the  characteristics  of  the  species. 


THE  PRODUCTION  OF  DOMESTIC  RACES.  1 5 

Neither  change  la  the  relative  numbers  in  which  we  choose  to  raise 
two  species,  nor  diversity  of  success  in  raising  those  that  are  equally 
desired,  can  be  the  cause  of  transformation  of  species,  as  long  as  the 
proportions  in  the  variations  of  the  intergenerating  forms  of  each 
species  remain  unchanged.  Diminution  and  extinction  on  the  one 
hand,  or  increase  and  unprecedented  multiplication  on  the  other, 
are  alike  without  effect  in  changing  the  character  of  a  race,  or  a 
species,  as  long  as  the  proportionate  propagation  of  the  different  inter- 
generating forms  or  variations  that  constitute  the  race  or  species 
remains  unchanged. 

In  other  words,  the  selection  that  produces  transformation  is  not 
the  selection  of  one  segregated  race  or  species  to  the  exclusion  of 
another,  but  the  selection,  from  the  offspring  of  one  intergenerating 
race,  of  certain  forms  that  do  not  represent  the  average  character  of  the 
race,  and  giving  to  them  either  exaggerated  or  exclusive  opportunity 
to  propagate  the  race.  Failure  to  recognize  this  distinction  has  been 
a  source  of  confusion  in  the  reasoning  of  certain  writers  on  evolution. 

Briefly  stated,  the  process  on  which  breeders  chiefly  rely  for  trans- 
forming a  domestic  race,  without  dividing  it  into  divergent  races,  is 
unbalanced  propagation  through  exclusive  breeding  from  individ- 
uals whose  average  endowment,  in  some  chosen  character,  is  above 
the  average  endowment  of  the  whole  race.  This  is  often  secured  by 
destroying  the  least  acceptable  individuals  before  they  propagate. 
Of  the  American  bison  there  are  supposed  to  be  about  600  surviving 
individuals.  If  these  were  all  brought  together  in  one  park,  and  if 
in  each  successive  generation  all  those  that  ranked  above  the  average 
of  their  generation  in  length  of  horns  were  slaughtered  before  they 
came  to  maturity,  there  can  be  no  doubt  that  after  many  generations 
the  whole  species  would  be  transformed  into  one  possessing  shorter 
horns  than  those  that  now  characterize  the  species. 

This  process  would  be  one  method  of  securing  what  is  usually 
called  selection  in  the  breeding  of  animals ;  and  selection  is  regarded 
as  the  chief  means  by  which  the  different  races  of  domestic  animals 
have  been  produced.  It  should,  however,  be  noted  that  the  success 
of  this  process  of  transforming  the  species  depends  on  certain  condi- 
tions that  are  not  secured  by  the  process  of  selecting.  It  is  neces- 
sary that  there  should  be  in  each  generation  such  a  difference  in  the 
length  of  the  horns  that  it  is  possible  to  tell  with  certainty  which  are 
above  and  which  below  the  average.  Again,  there  must  be  such  a 
degree  of  fertility  and  such  success  in  attaining  maturity  that  there 
shall  be  a  considerable  surplus  of  individuals  of  both  sexes  that  may 
be  slaughtered  without  gradually  exterminating  the  race.     Again,  it 


1 6  BIONOMIC  LAWS. 

should  be  observed  that  it  is  not  every  kind  of  selection  that  produces 
transformation.  It  is  only  as  selection  results  in  the  preservation  of 
other  than  average  forms  that  it  has  any  influence  in  transforming  a 
race.  The  selection  of  average  forms  for  propagation  tends  to  pro- 
duce stability  of  type ;  and  the  selection  of  extreme,  but  of  opposite, 
and,  therefore,  balanced  deviation  from  the 'type  produces  fluctuating 
variation ;  but  unbalanced  selection,  that  is,  propagation  from  forms 
whose  average  character  differs  froni  the  average  character  of  the 
race,  changes  in  some  degree  the  average  character  of  the  race  in  the 
next  generation.  Whenever  this  takes  place,  whether  it  be  by  the 
design  of  man  or  not,  there  transformation  takes  place. 

Unbalanced  artificial  selection  is  not  the  only  principle  producing 
the  unbalanced  propagation  of  the  variations  of  domestic  races.  Un- 
balanced natural  selection  caused  by  change  in  climate  or  in  other 
external  conditions,  and  resulting  in  the  superior  success  of  other 
than  average  forms,  will  also  produce  unbalanced  propagation  of 
domestic  as  well  as  of  wild  races.  Again,  it  may  be  that  some  form 
of  variation  that  is  above  the  average  in  strength  or  skill,  or  in  the 
length  of  natural  weapons,  or  in  the  beauty  of  its  adornments,  will 
gain  an  advantage  over  its  fellows  in  the  appropriation  of  food  or 
in  winning  mates,  and  so  become  subject  to  some  form  of  reflexive 
selection,  by  which  unbalanced  propagation  is  produced. 

There  may  also  arise  unbalanced  elimination,  when,  through  some 
overwhelming  catastrophe,  a  large  portion  of  the  domestic  stock  is 
destroyed,  and  the  remaining  individuals  that  propagate  do  not  repre- 
sent the  average  characteristics  of  the  race.  This  may  be  called 
indiscriminate  elimination.  Indiscriminate  elimination  arises  when 
war,  famine,  pestilence,  or  earthquake  falling  upon  a  tribe  of  men 
results  in  the  indiscriminate  destruction  of  nearly  all  of  their  domestic 
animals;  and  in  many  of  these  cases  the  surviving  individuals  from 
which  the  stock  is  afterward  propagated  do  not  represent  the  average 
character  of  the  previous  stock. 

Again,  some  variation  of  the  stock  may  be  endowed  with  a  degree 
of  fecundity  decidedly  above  the  average  fecundity  of  the  rest  of  the 
stock;  and,  if  the  form  possessing  this  superior  fecundity  is  as  well 
adapted  as  other  forms  to  meet  the  desires  of  those  who  raise  the 
creatures,  unbalanced  propagation  will  take  place,  and  the  average 
character  of  the  stock  will  be  changed.  In  my  paper  on  Intensive 
Segregation*  I  call  this  principle  fecundal  transformation.  Karl 
Pearson  has  discussed  this  principle  under  the  title  of  "reproductive 


*  See  Appendix  II. 


THE  PRODUCTION  OF  DOMESTIC  RACES.  l^ 

selection,"  in  a  very  interesting  chapter  of  his  volume  entitled  "The 
Chances  of  Death  and  Other  Studies  in  Evolution."  I  fully  agree 
with  this  author  in  the  emphasis  he  puts  on  the  importance  of  a  care- 
ful statistical  investigation  of  the  subject;  but  I  think  the  term  he 
has  chosen  would  naturally  apply  to  sexual  and  impregnational  selec- 
tion as  well  as  to  this  form  of  selection  which  is  dependent  on  degrees 
of  fertility.  If  these  are  all  to  be  called  forms  of  selection,  I  would 
suggest  that  the  special  principle  under  consideration  might  be  desig- 
nated fecundal  selection,  and  its  effect  on  the  group  might  be  called 
fecundal  transformation. 

3.  The  Divergence  of  Races. 

In  order  to  produce  two  or  more  divergent  breeds  from  one  breed, 
it  is  necessary,  first,  that  the  original  stock  should  be  divided  into 
separate  portions  that  are  prevented  from  crossing  (this  is  conven- 
iently called  isolation) ;  and,  second,  that  there  should  be  some  cause 
transforming  one  or  more  of  these  separated  portions.  Now,  the 
cause  producing  transformation  in  a  separated  portion  may  be  the 
incapacity  of  a  given  small  fragment  of  a  race  or  species  to  perpetuate 
the  original  average  character  of  that  race  or  species ;  or,  after  sepa- 
ration, the  portion  may  be  subjected  to  some  form  of  unbalanced 
selection. 

Returning,  for  illustration,  to  the  600  bison,  we  may  suppose  them 
to  be  indiscriminately  divided  into  two  isolated  herds  of  300  each,  in 
which  case  the  average  character  of  each  herd  would  probably  be 
nearly  the  same  as  that  of  the  other  herd,  and  the  descendants  of  the 
two  herds,  if  not  subjected  to  different  kinds  of  selection,  would  prob- 
ably present  no  important  differences,  at  least  for  many  generations. 
If,  however,  the  whole  herd  were  broken  up  into  pairs,  the  offspring 
of  the  pairs  forming  300  isolated  groups,  each  of  which  was  never 
allowed  to  cross  with  any  other  group,  we  should  probably  find  that 
perceptible  divergences  would  soon  present  themselves  in  some  of 
the  groups,  even  if  they  were  not  subjected  to  unlike  selection. 

Another  form  of  isolation,  still  more  effective  in  producing  diver- 
gence, would  be  gained  if  the  individuals  presenting  the  highest  de- 
gree of  some  special  kind  of  variation  were  brought  together  in  one 
group  that  was  prevented  from  crossing  with  the  others.  The 
division  of  organisms  which  have  descended  from  one  original  inter- 
generating  group  into  two  or  more  groups  that  do  not  possess  the 
same  average  character,  and  that  lack  either  the  capacity,  inclination, 
or  opportunity  for  intergenerating,  I  call  segregation.  Whenever 
there  is  a  closer  resemblance  between  the  members  of  an  intergenerat- 


1 8  BIONOMIC  IvAWS. 

ing  group  than  between  them  and  the  members  of  some  other  group 
with  which  free  crossing  has  been  interrupted,  there  segregate  breed- 
ing or  segregation  exists.  If  it  were  possible  to  divide  the  600  bison 
into  two  completely  equivalent  groups,  the  isolation  of  these  two 
groups  would  not  involve  segregation ;  but  the  indiscriminate  division 
of  any  intergenerating  group  into  two  or  more  isolated  groups 
usually  involves  more  or  kvSS  difference  in  the  groups,  and,  therefore, 
more  or  less  segregation. 

If  we  carefully  consider  the  process  by  which  the  different  domestic 
races  of  any  species  have  been  produced,  we  shall  find  that  the  isola- 
tion of  each  race  from  every  other  race  has,  in  every  case,  been  a 
prime  factor.  Until  modern  times  the  hostility  of  different  tribes  of 
men  and  the  want  of  free  commerce  between  nations  have  secured  the 
isolated  breeding  of  the  domestic  races  under  the  care  of  different 
tribes  and  peoples.  Now,  according  to  the  principle  I  have  just 
pointed  out,  the  initial  differences  between  those  portions  make  them 
more  or  less  segregated  groups  whenever  free  crossing  between  the 
portions  is  cut  off.  But  this  initial  segregation  is  soon  intensified  by 
the  transforming  influences  to  which  the  different  portions  are  sub- 
jected. As  each  portion  is  subjected  to  the  care  of  a  separate  tribe 
of  men  who  preserve  such  individuals  of  the  offspring  as  best  suit 
their  purposes  or  fancies,  and  as  the  individuals  thus  preserved  sel- 
dom represent  the  average  form  of  the  wild  species,  transformation 
is  soon  produced.  Each  isolated  group,  if  it  survives  under  its  new 
conditions,  must  produce  forms  increasingly  adapted  to  meet  the 
desires  of  those  who  care  for  them ;  and  even  when  those  on  whom  they 
depend  have  no  idea  of  developing  new  characteristics  by  selection, 
unconscious  selection  usually  takes  place.  If  the  selected  form  is  not 
the  average  form,  transformation  necessarily  follows.  But  as  we  are 
now  considering  the  process  by  which  divergent  evolution  has  been 
produced  in  domestic  races,  the  important  point  is,  not  that  trans- 
formation is  usually  produced  by  domestication,  but  that,  when  this 
cause  of  transformation  modifies  continuously  isolated  portions  of 
the  same  species,  the  result  is  always  divergent  and  not  parallel.  Ac- 
count for  it  as  we  may,  when  a  domestic  breed  has  been  transformed 
during  isolation,  the  transformed  portions  are  always  found  to  be 
more  or  less  unlike ;  and  this  is  so  even  when  the  physical  conditions 
are  the  same,  and  when  the  persons  on  whom  the  selection  has  devolved 
are  representatives  of  the  same  race. 

I  think  it  will  be  found  that  independent  transformation  (that  is, 
transformation  during  isolation),  is  always  divergent  and  never  com- 
pletely parallel ;  and  I  believe  this  to  be  so  whether  the  transforma- 


THE  PRODUCTION  OF  DOMESTIC  RACES.  I9 

tion  is  due  to  unbalanced  natural  selection  or  to  some  other  principle, 
as,  for  example,  the  direct  effects  of  use  or  disuse,  or  to  indiscriminate 
elimination.  Just  as  indiscriminate  isolation  may  produce  unbal- 
anced groups,  and,  therefore,  segregation,  so  indiscriminate  destruc- 
tion in  the  isolated  groups  is  liable  to  produce  unbalanced  propaga- 
tion of  diverse  kinds,  and  so  divergent  transformation  with  intensive 
segregation.  If  animosities  arise  between  two  sections  of  a  tribe, 
the  domestic  animals  in  the  care  of  the  two  sections,  though  com- 
pletely isolated,  may  present  no  apparent  differences  till  famine  or 
some  other  calamity  leads  to  the  indiscriminate  slaughter  of  all  but  a 
pair  or  two  of  some  species  in  one  of  those  districts.  This  small 
fragment  will,  in  many  cases,  be  unable  to  reproduce  in  all  respects 
the  average  character  of  the  original  race,  and  will  become  quite 
perceptibly  divergent.  If  heavy  but  indiscriminate  elimination  falls 
upon  the  representatives  of  a  given  species  in  both  sections  of  the 
country,  the  divergence  in  the  isolated  groups  will  be  likely  to  be 
somewhat  greater  than  if  but  one  section  suffers.  This  principle 
differs  from  natural  selection  in  that  the  exclusion  is  indiscriminate 
instead  of  discriminate.  Extreme  elimination,  leaving  only  a  very 
small  remnant,  is  always  unbalanced  elimination  as  regards  some  of 
the  characters  and,  therefore,  tends  to  produce  transformation. 

Again,  the  effects  of  crossing  between  different  strains  and  races  of 
the  same  species  may  occur  in  different  degrees  in  the  different  dis- 
tricts over  which  a  species  is  distributed,  and  may,  therefore,  result 
in  divergences  in  different  districts.  This  principle  I  have  called 
amalgamational  transformation. 

4.  The  Stability  of  Races. 

For  the  preservation  of  a  given  race-type  it  is  usually  considered 
necessary  to  exclude  from  propagation  a  certain  proportion  of  the 
variations  that  fall  below  the  average  which  constitutes  the  type.  The 
degree  of  exclusive  breeding  that  is  needed  to  maintain  the  present 
average  depends  upon  the  stability  of  the  type,  that  is,  the  weakness 
of  the  tendency  to  revert  to  forms  possessed  by  more  or  less  remote 
ancestors.  Whether  a  type  may  become  so  fully  established  as  to 
maintain  a  constant  average  without  any  tendency  to  reversion,  is 
perhaps  an  open  question ;  but  in  the  case  of  the  goose,  which  is  one 
of  the  most  stable  of  domestic  species,  it  is  not  certain  that  what  has 
'been  called  the  birth  average  more  closely  resembles  ancestral  types 
than  does  the  average  that  comes  to  maturity  and  propagates  the 
sp>ecies.  The  vitality  of  those  that  live  and  propagate  is  undoubtedly 
higher  than  that  of  the  whole  generation;  but  this  does  not  prove 


20  BIONOMIC  LAWS. 

that  selection  is  necessary  to  maintain  the  distinctive  characters  of 
the  species.  The  effect  of  cessation  of  selection  is  a  subject  of  great 
interest,  on  which  further  light  is  needed.  In  dealing  with  an  ordi- 
nary species,  the  breeder  assumes  that  the  exclusive  propagation  of 
average  forms  will  tend  to  produce  stability  of  type  rather  than  rever- 
sion ;  and  he  ignores  any  difference  that  may  exist  between  the  birth- 
average  and  the  adult-average.  His  only  hope  of  producing  diver- 
gent races  is  found  in  the  separate  breeding  of  forms  that  are  manifest 
departures  from  both  the  birth-average  and  the  adult-average  in 
some  given  direction.  If  sheep  with  long  and  fine  wool  are  desired, 
he  selects  sheep  possessing  these  qualities  in  the  highest  degree  as 
the  ones  from  which  to  raise  his  flocks. 

5.   The  Amalgamation  of  Races. 

Once  more,  the  breeder  finds  that  the  free  crossing  of  different 
races  introduces  great  variation,  with  the  breaking  down  of  race  dis- 
tinctions. The  interfusion  of  races,  with  the  strange  preponderating 
influence  that  belongs  to  some  races,  or  sometimes  to  one  sex  of  a 
given  race,  is  a  subject  that  is  worthy  of  fuller  study  than  has  yet 
been  given  to  it. 

6,  The  Infltience  of  Acquired  Characters  on  Racial  Characters. 

Fully  satisfactory  proof  or  disproof  of  the  direct  inheritance  of 
acquired  characters  has  not  yet  been  accumulated;  but  as  I  pointed 
out  in  my  paper  on  "Intensive  Segregation,"  reproduced  in  Appendix 
II  of  this  volume,  their  indirect  influence  on  inheritance  is  certain; 
for  "All  diversities  of  environal  selection  that  do  not  vary  according 
to  differences  in  the  environment  must  be  classed  as  diversities  of 
active  selection  (or  endonomic  selection,  as  I  sometimes  call  the  prin- 
ciple) ,  for  they  must  have  originated  in  some  variation  of  the  powers 
of  the  organism,  or  in  the  diversity  of  uses  to  which  it  has  put  its 
powers."*-  In  the  same  paper  I  further  called  attention  to  the  fact 
that  where  a  group  of  species  possessing  extremely  limited  powers 
and  opportunities  for  migration  are  distributed  in  a  district,  where 
all  the  other  species  of  both  plants  and  animals  have  the  usual 
powers  and  opportunities  for  migration,  here  we  find  the  group,  with 
limited  faciUties  for  migrating,  varying,  though  the  environment, 
both  physical  and  organic,  is  essentially  the  same.  Observation  also 
teaches  us  that  when  a  gravid  female  of  a  variable  species  is  isolated 

*  The  small  species  of  Achatinella  found  in  the  valleys  in  the  northwestern  por- 
tion of  the  island  of  Oahu  have  different  habits  of  feeding  from  those  of  larger  size 
found  near  the  eastern  end  of  the  island.  (See  Plate  II  and  the  explanation 
of  the  same,  Chapter  IV.) 


THE  PRODUCTION  01^  DOMESTIC  RACES.  21 

in  a  region  furnishing  the  same  environment  as  the  original  home 
from  which  it  has  been  transported,  some  pecuUar  habit  of  feeding, 
acquired  in  the  original  home,  may  become  the  transmitted  habit 
determining  the  life  of  the  new  colony,  and  so  determine  the  forms  of 
selection  to  which  the  new  group  is  subjected.  This  form  of  selection 
I  call  active  or  endonomic  selection.  Again,  there  is  reason  to  believe 
that  the  different  forms  of  reflexive  selection,  of  which  sexual  selection 
is  the  most  familiar  example,  may  gradually  change  in  an  isolated 
portion  of  a  species  without  depending  on  change  in  the  environment. 
In  these  and  other  ways  I  have  shown  that  many  groups  of  organisms 
are  undergoing  transformations  that  can  not  be  attributed  to  changes 
in  the  environment.  The  subject  has  been  presented  in  several 
forms  in  the  paper  referred  to  above,  reproduced  in  Appendix  II.  As 
a  further  illustration  of  my  idea,  I  would  say  that  I  think  there  is  no 
reason  to  claim  that  our  arboreal  ancestors  were  forced  to  forsake  the 
traditions  of  their  fathers,  through  the  failure  of  the  forest  to  grow,  or 
through  any  other  change  in  the  environment.  It  is  more  natural  to 
suppose  that  the  great  prosperity  of  our  forebears  in  the  forest  regions 
increased  their  numbers  till  it  became  desirable  that  some  new  sphere 
of  activity  should  be  discovered.  The  rich  rewards  that  came  to  the 
more  enterprising  ones,  who  searched  the  open  country  by  day  and 
hid  in  the  caves  at  night,  was  probably  the  beginning  of  the  change 
that  has  led  to  the  separate  methods  of  use  for  our  fore  limbs  and  our 
hind  limbs.  The  great  advantage  of  standing  erect  and  taking  a 
broad  look  over  the  fields  of  deep  grass  started  selection  toward 
human  feet.  This  view  of  the  course  of  evolution  reveals  the  influ- 
ence of  habit  in  controlling  selection,  and  so  finally  in  controlling 
inheritance.  The  frequent  control  of  the  form  of  survival  by  the 
activities  in  the  organism,  and  not  by  change  of  activities  in  the  en- 
vironment, was  emphasized  in  my  papers  published  by  the  Linnaean 
Society ;  and  more  recently  the  importance  of  individual  adjustment 
to  sudden  change,  through  the  securing  of  time  for  "  coincident 
variation,"  has  been  pointed  out  by  Lloyd  Morgan*  and  others. 
As  the  processes  mentioned  under  these  six  heads,  when  brought 
about  in  domestication,  produce,  in  the  first  case,  either  continuance 
or  extermination  of  the  race;  in  the  second,  simple  transformation; 
in  the  third,  divergence;  in  the  fourth,  increased  stability;  in  the 
fifth,  increased  variation  with  blending  of  types;  and  in  the  sixth, 
transformation  in  the  organism  that  does  not  depend  on  change  in 
the  environment,  we  have  reason  to  expect  that  when  produced  by 


*See  "  Habit  and  Instinct,"  1896,  pp.  312!?. 


22  BIONOMIC  LAWS. 

natural  causes  the  results  will  be  essentially  the  same.  These  may 
all  be  classed  as  processes  of  evolution,  that  is,  processes  by  which  a 
type  is  either  preserved  or  more  fully  established  or  intensified,  or 
through  which  it  unfolds  divergent  forms,  or  through  which  it  is  com- 
mingled with  other  types.  In  the  whole  process  of  organic  evolution 
the  fundamental  activity  is  the  reproduction  of  individuals,  endowed 
with  the  double  acting  quality  of  variation  and  heredity,  which  is 
constantly  controlled  and  shaped  by  the  more  or  less  rigid  realization 
of  the  law  of  segregate  breeding,  or  the  intergeneration  of  like  with 
like  with  the  prevention  of  crossing  between  unlike  groups.  As  we 
have  seen  in  the  brief  description  of  the  production  of  domestic  races 
just  given,  there  are  several  different  methods  by  which  unbalanced 
propagation  may  be  brought  about,  and  wherever  unbalanced  propa- 
gation is  produced,  there  transformation  is  the  result,  and  there  segre- 
gate breeding  is  intensified.  Again,  there  are  several  methods  by 
which  a  single  intergenerating  group  may  be  divided  into  two  or 
more  groups,  with  free  intergeneration  within  each  group,  while  there 
is  prevention  of  crossing  between  the  groups;  and  some  form  of  this 
process  of  isolation  is  an  essential  condition  for  divergent  evolution ; 
for  without  isolation,  variations  of  divergent  types  can  not  be  accum- 
ulated. In  order  to  understand  the  method  of  evolution,  it  is  neces- 
sary to  keep  in  mind  the  initial  segregation  produced  by  the  different 
forms  of  isolation,  and  the  intensified  segregation  produced  by  the 
different  forms  of  selection  and  other  influences  (including  diver- 
sity of  habits),  which  insure  the  transformation  of  the  isolated  group. 
After  this  brief  survey  of  the  causes  of  divergence  in  domestic  ani- 
mals, we  will  now  turn  our  attention  to  divergent  types  that  have 
arisen  under  natural  conditions. 


CHAPTER  III. 

THE  EVOLUTION  OK  NATURAL  SPECIES. 

I.     Unity  and  Diversity. 

The  great  problems  of  biology  are  found  in  the  unity  and  diversity 
of  organisms.  What  is  the  nature  and  origin  of  the  unity?  What 
the  nature  and  origin  of  the  diversity?  And  what  the  relation  of  each 
of  these  classes  of  facts  to  the  other? 

1 .  Darwin's  Explanation  of  the  I  'nity  0}  Organic  Forms  has  been  widely 
adopted  by  naturalists  as  by  far  the  most  probable  theory;  but  his 
theory  of  the  causes  of  the  diversity  of  these  forms  lias  not  met  with  the 
same  general  acceptance. 

He  teaches  that  the  variation,  on  which  natural  selection  acts,  is, 
for  the  most  part,  minute  and  indefinite  variation  in  any  and  every 
direction,  and  that  the  progressive  accumulation  of  one  series  of  varia- 
tions, all  tending  to  the  production  of  a  new  species,  is  due  to  nat- 
ural selection.  If  all  the  offspring  of  any  species  were  allowed  to 
live  out  the  full  measure  of  their  days  and  should  have  an  equal 
chance  to  produce  descendants,  there  would  be,  according  to  his 
theory,  no  tendency  to  a  change  of  form;  for  variations  of  every 
kind,  having  an  equal  chance,  would  neutralize  the  divergent  tenden- 
cies of  each  other  in  the  general  result. 

Fluctuating  variability,  producing  individual  variations,  is  attrib- 
uted for  the  most  part  to  the  indefinite  and  indirect  influence  of 
changed  conditions  upon  the  organism,  the  forms  of  variation  being 
chiefly  determined  by  the  nature  of  the  organism;  but  the  trans- 
formation of  a  group  of  associated  individuals  is  attributed  to 
natural  selection,  which  is  the  effect  of  external  conditions  tending 
to  give  advantage  to  the  form  of  individual  variation  that  is  best 
adapted  to  these  conditions.  He  says,  "Chance  variation  [that  is, 
variation  unaided  by  natural  selection]  would  never  account  for  so 
habitual  and  large  degree  of  difference  as  that  between  the  species  of 
the  same  genus."  Not  only  the  existence  of  the  various  species  of 
each  genus,  but  the  precise  form  of  each  species,  and  the  instincts 
guiding  each,  are,  therefore,  attributed  to  the  determining  power  of 
conditions  outside  of  the  organism,  allowing  of  but  one  line  of  trans- 
formation in  the  descendants  of  any  one  species  exposed  to  the  same 
conditions.     In  order  that  any  other  line  of  transformation  should  be 

23 


24  THE  EVOLUTION  OF  NATURAL  SPECIES. 

followed  by  the  descendants  of  the  same  species,  he  considers  it  nec- 
essary that  they  should  be  brought  under  the  influence  of  different 
conditions.  In  other  words,  divergence  of  character  presupposes  ex- 
posure to  diverse  external  conditions;  and  to  account  for  the  various 
forms  presented  by  the  different  species  of  the  same  genus,  he  assumes 
that  they  must  have  been  subjected  to  different  forms  of  natural 
selection.  This  theory  of  evolution  is  in  strong  contrast  with  the 
theory  which  attributes  the  main  factors  to  powers  residing  in  the 
organism. 

2.  Divergence  through  Variation  Protected  by  Isolation,  and  Unity 
through  Community  of  Descent. 

(i)  When  water  flows  down  the  side  of  a  hill  from  any  given  point, 
there  is  usually  but  one  path  that  it  can  take;  but  when  an  ani- 
mal with  the  power  of  locomotion  makes  the  same  descent  there  may 
be  many  paths  equally  open  to  him,  and  different  individuals  of  the 
same  species,  if  making  the  descent,  will  often  take  different  paths. 
The  course  of  the  water  is  determined  by  laws  that  allow  of  no  devia- 
tion; the  course  of  the  animal  is  determined  by  laws  that  allow  of 
considerable  diversity  in  their  results ;  nevertheless,  it  is  in  a  measure 
determined,  and  the  laws  that  determine  it  are  found  in  the  relation 
of  the  powers  of  the  animal  to  the  natural  conditions  of  the  different 
paths.  Paths  leading  down  a  precipitous  descent  may  be  the  short- 
est and  best  for  the  snail,  but  impassable  for  the  horse ;  still  both  the 
horse  and  the  snail  may  find  many  paths  that  are  available,  and  per- 
haps several  that  are  equally  available.  The  rash  horses  that  attempt 
the  precipitous  paths  break  their  necks,  while  the  cautious  horses 
that  take  the  many  safe  paths  are  unharmed.  But,  shall  we  therefore 
say  that  the  path  taken  by  each  horse  making  a  safe  descent  is 
wholly  determined  by  external  conditions?  If  precipices  prevent 
descent  by  every  path  but  one,  there  is  no  opportunity  for  varying 
the  course,  and  we  regard  it  as  being  determined  by  the  external  con- 
ditions ;  but  when  the  way  is  open  in  many  directions,  we  would  say 
that  the  one  horse  being  thirsty  took  the  path  that  leads  to  the 
spring,  another  being  hungry  chose  the  shortest  road  to  the  clover 
field,  thus  attributing  the  course  of  the  animal  to  conditions  found  in 
the  animal. 

This  well  illustrates  what  I  believe  is  true  concerning  the  diver- 
gence of  character  that  results  in  different  specific  forms.  I  believe 
that  the  quality,  the  diversity,  and  the  rapidity  of  the  variation  depend 
chiefly  upon  the  nature  of  the  organism;  and  that  while  the  nature  of 
the  external  conditions  has  power  to  winnow  out  whatever  forms  are 


UNITY  AND  DIVERSITY.  25 

least  fitted  to  survive,  there  will  usually  remain  a  number  of  varieties 
equally  fitted  to  survive ;  and  that  throiigh  the  law  of  segregation  con- 
stantly operating  in  a  species  distributed  in  isolated  groups  over  a  consid- 
erable area  these  varieties  continue  to  diverge  both  in  form  and  in  habits 
till  separate  species  are  fully  established,  though  the  external  conditions 
are  the  same  throughout  the  whole  area  occupied  by  the  diverging 
forms. 

(2)  Uniformity,  on  the  other  hand,  is  the  result  of  community  of 
descent,  and  varies  directly  as  the  diffusion  of  consanguinity,  or  the 
amount  of  evenly  distributed  intercrossing.  Isolation  and  intergenera- 
tion  are  opposing  factors,  the  one  tending  to  divergence  of  character, 
the  other  to  uniformity ;  but  the  influence  of  natural  selection  may  be 
in  either  direction,  according  as  its  action  is  diverse  in  different  parts  of 
the  area  or  uniform  throughout  the  whole  area.  When  animal  immi- 
grants enter  a  new  region  in  which  not  only  the  climate  but  the  flora 
and  fauna  differ  widely  from  those  found  in  the  home  of  the  species, 
the  probability  is  that  they  will  succumb  without  leaving  descendants 
or  that  their  descendants  will  diminish  with  each  generation  till  they 
disappear ;  but  if  the  struggle  is  not  too  severe,  the  species  will  survive, 
and,  if  isolated,  the  divergence  of  character  may  be  greatly  accelerated 
by  the  effects  of  natural  selection;  for  the  forms  that  will  be  best 
fitted  to  succeed  in  life  and  to  propagate  their  kind  will  differ  in  the 
two  regions  according  to  the  conditions  under  which  they  have  to 
compete;  and  the  intermediate  forms  that  are  less  fitted  will  be 
weeded  out,  and  their  influence  in  crossing  with  the  diverging  kinds 
that  survive  will  be  removed.  It  will  be  seen  that  natural  selection 
acts  as  a  divergent,  not  by  its  own  inherent  power,  but  by  removing 
the  intermediate  varieties  and  thereby  preventing  their  influence  in 
crossing;  but  if  the  competition  is  severe  and  uniform  throughout 
the  area  occupied  by  any  species,  its  influence  will  be  to  lessen 
divergence. 

That  this  double  relation  of  natural  selection  to  divergence  on  one 
side,  and  to  uniformity  on  the  other,  was  partially  apprehended  by 
Darwin,  appears  from  his  brief  paragraph  on  Polymorphic  Genera, 
and  his  fuller  statements  concerning  the  extinction  of  intermediate 
forms  by  means  of  natural  selection;  but  the  quotation  given  near 
the  beginning  of  this  chapter  shows  that  he  did  not  reach  the 
conclusion  which  lay  but  one  step  beyond,  and  to  which  his  facts  so 
clearly  point.  He  observed  that  polymorphic  genera  are  probably 
most  variable  in  the  characters  that  are  neither  useful  nor  injurious 
to  the  species,  and  are,  therefore,  free  from  the  influence  of  natural 
selection ;  and  again,  in  another  place,  he  observes  that  large  genera 


26  THB  EVOLUTION  OF  NATURAL  SPECIES. 

are  usually  variable,  that  is,  polymorphic,  and  that  these  same  genera 
are  the  ones  in  which  the  production  of  new  species  is  most  rapidly 
progressing;  but  he  has  nowhere  drawn  the  conclusion  that  freedom 
from  rigid  natural  selection  can  in  any  way  favor  the  production  of 
new  varieties  and  species.  On  the  contrary,  he  teaches  that  it  is  only 
through  the  agency  of  diversity  in  natural  selection  that  individual 
variations  can  be  accumulated  in  diverging  lines  that  become  more 
and  more  distinct.     (See  Origin  of  Species,  Chapter  IV.) 

3.  Facts  in  the  Distribution  of  Hawaiian  Snails. 

It  was  through  the  study  of  island  fauna  that  I  was  first  led  to 
doubt  the  correctness  of  Darwin's  theory  at  this  point.  The  terres- 
trial mollusks  of  the  West  Indies  present  important  differences  as  we 
pass  from  island  to  island,  but  it  was  in  the  Hawaiian  Islands  that  I 
found  the  greatest  difference  in  the  species  inhabiting  the  forests  in 
different  parts  of  the  same  island.  The  remarkable  features  in  the 
distribution  and  affinities  of  these  forms  will  be  most  easily  presented 
by  giving  a  brief  statement  of  some  of  the  facts  relating  to  those 
found  on  the  island  of  Oahu.  This  island,  about  45  miles  in  length 
and  20  miles  in  width,  is  inhabited  by  over  200  species  of  land  snails, 
represented  by  800  or  i  ,000  varieties ;  and  these  are  nearly  all  confined 
to  the  forests  covering  two  ranges  of  mountains,  the  one  1 5  or  20  miles 
and  the  other  35  miles  in  length.  But  the  most  remarkable  fact  is  not 
the  great  number  of  species  and  varieties  inhabiting  this  small  area, 
nor  yet  that  all  of  them  (with,  perhaps,  one  or  two  exceptions)  are 
peculiar  to  this  island ;  but  that  each  of  these  forms  is  confined  to  only 
a  small  section  of  this  small  area.  Not  only  are  the  species  on  each 
of  the  ranges  of  mountains  different,  but  those  found  on  one  range 
and  inhabiting  one  continuous  region  of  forest  are  not  distributed  at 
random  over  that  region.  On  the  contrary,  each  valley  not  more  than 
half  a  mile  in  width  and  perhaps  two  miles  in  length  has  its  own 
peculiar  varieties,  and  in  some  cases  its  own  species,  which  are  found 
nowhere  else. 

As  the  explorer  passes  from  valley  to  valley  he  will  find  six  or  seven 
quite  distinct  groups  of  forms,  each  group  being  a  genus  or  a  sub- 
genus of  the  one  family  of  Achatinellidae.  Taking  any  one  genus  and 
tracing  its  distribution  from  valley  to  valley,  he  will  find  that,  as  far 
as  it  extends,  it  is  represented  in  each  valley  by  one  or  more  closely 
allied  species,  each  species  being  represented  by  several  varieties. 
One  species  may  be  confined  to  a  single  valley,  or  it  may  extend  over 
several,  being  represented  in  each  by  varieties  peculiar  to  that  valley. 
The  more  widely  divergent  forms  of  one  group  or  genus  will  be 


UNITY  AND  DIVERSITY.  27 

found  in  the  valleys  that  are  most  distant  from  each  other.  That  is, 
if  the  genus  is  present  in  all  the  valleys,  the  most  divergent  forms 
will  be  found  at  the  opposite  ends  of  the  mountain  range,  while  in- 
termediate forms  will  be  found  in  the  intermediate  valleys.  Allied 
species  occupying  neighboring  localities  pass  into  each  other  by  many 
gradations  of  form  and  color,  while  those  that  are  separated  by  a  dis- 
tance of  8  or  lo  miles  or  more  can  not  be  connected  by  minute  grada- 
tions without  bringing  in  some  of  the  forms  found  in  the  intermediate 
territory. 

Such  are  the  main  facts  concerning  these  forms  when  viewed  in  their 
relation  to  each  other.  I^et  us  now  consider  the  external  conditions. 
Does  the  theory  that  all  divergence  of  character  is  due  to  exposure 
to  diverse  conditions  find  confirmation,  or  the  opposite,  in  the  facts 
connected  with  these  Hawaiian  snails  ? 

4.  Diversity  of  Natural  Selection  not  a  Sufficient  Explanation  of  the 
Diversity  of  Species. 

Natural  selection  depends  upon  external  conditions  which  are 
either  favorable  or  unfavorable  to  the  success  and  propagation  of 
the  organisms  under  consideration;  and  difference  in  natural  selec- 
tion must  depend  upon  difference  in  the  nature  of  the  external  condi- 
tions that  affect  survival.  Now,  returning  to  the  case  of  the  nearly 
allied  arboreal  species  in  the  valleys  near  Honolulu,  can  we  find  any 
diversity  affecting  survival  in  the  conditions  to  which  they  are  ex- 
posed? In  many  cases  we  find  them  occupying  the  same  species  of 
trees,  and,  accordingly,  if  their  habits  of  feeding  are  different,  we 
must  attribute  this  difference  to  spontaneous  variation  rather  than 
to  the  influence  of  external  conditions.  Extending  our  observations 
to  the  climate  and  soil,  we  find  the  conditions  unvaried,  we  might 
well  say,  identical ;  for  the  geological  foundation  of  the  whole  moun- 
tain range  is  volcanic  basalt  without  the  least  limestone,  and  the  soil 
in  these  rugged  valleys  is  not  varied  by  the  presence  even  of  volcanic 
ash,  while  the  conditions  of  heat  and  moisture  are  the  same  on  the 
same  side  of  the  mountain  crest.  The  vegetation  in  each  valley  is 
essentially  the  same,  and  distributed  in  a  similar  way;  for  certain 
shrubs  and  trees  occupy  the  lower  grounds  and  others  the  steep  slopes 
and  ridges  that  rise  above.  If  the  species  of  mollusks  which  we  are 
studying  have  any  enemies  they  are  found  in  the  forest  regions 
throughout  the  island.  No  insect  or  reptile,  no  bird  or  mammal, 
found  on  the  island  is  limited  to  a  district  of  only  2  or  3  miles  extent. 

As  we  fail  to  find  any  cause  for  the  divergences  of  character  in  the 
external  conditions,  we  must  believe  either  that  the  conditions  are 


28  THE  EVOLUTION  OJf  NATURAI,  SPECIES. 

more  diversified  than  they  appear  to  be,  or  that  the  causes  of  change 
in  these  cases  belong  wholly  to  the  nature  of  the  organism.  That  the 
former  supposition  is  not  the  true  one  seems  to  me  to  be  sufficiently 
proved  by  the  following  facts  and  considerations : 

(i)  If  the  divergence  of  character  was  due  to  difference  of  natural 
selection  resulting  from  difference  in  external  conditions,  we  should 
expect  that  the  distribution  of  species  would  bear  some  marked  rela- 
tion to  the  amount  of  rainfall,  which,  owing  to  the  northeast  trade 
winds,  is  considerably  greater  on  the  northeast  side  of  the  mountain 
range  than  on  the  southwest  side.  On  the  contrary,  we  find  that 
species  of  the  same  group,  found  in  valleys  on  the  same  side  of  the 
range,  but  30  or  35  miles  apart,  are  far  more  divergent  from  each 
other  than  are  those  found  on  opposite  sides  of  the  range  but  at 
points  much  nearer.  Assuming  that  they  have  migrated  from  a  com- 
mon center,  the  distance  between  two  species  measures  in  a  rough 
way  the  relative  number  of  generations  that  have  passed  since  their 
ancestors  parted  company,  and  the  degree  of  divergence  is  in  propor- 
tion to  the  time  and  degree  of  separation  rather  than  in  proportion  to 
the  degree  of  difference  in  external  conditions. 

(2)  This  law  of  distribution  is  found,  not  simply  in  the  case  of  a 
few  related  forms,  in  which  it  might  be  supposed  that  the  diversity 
of  conditions  was  real,  though  not  apparent,  but  is  the  general  law 
according  to  which  the  200  species  and  800  or  i  ,000  varieties  of  Acha- 
tinellidae  found  on  this  island  are  for  the  most  part  distributed.  This 
law  also  controls  the  distribution  of  mollusks  on  the  neighboring 
islands  and  in  many  parts  of  the  world. 

(3)  If  we  assume  that  the  divergence  is  due  to  the  diversity  of 
natural  selection,  we  must  hypothecate  a  series  of  conditions  affecting 
survival  presenting  increasing  differences  with  each  additional  mile.* 

5.  The  Causes  of  the  Divergence  must  lie  in  the  Independent  Action  of 
the  Segregated  Sections  of  the  Original  Stock. 

For  my  part  I  find  it  easier  to  believe  that  the  causes  of  divergence 
of  character  in  these  forms  that  are,  so  far  as  we  can  discover,  exposed 
to  the  same  conditions,  exist  in  the  organism. 

(i)  We  know  that  the  individual  variations  in  specimens  of  one 
species  found  on  one  tree  are  often  very  considerable. 

(2)  Unless  the  degree  and  kind  of  variation  is  invariable  in  sepa- 
rated groups  of  the  same  species,  it  is  self-evident  that  there  must  be 
a  tendency  to  divergence  of  character. 


*  See  Plate  II,  figs.  1 1-25. 


SBLECTION  AS  AN  EXPLANATION.  29 

(3 J  So  far  as  statistical  observation  has  been  directed  to  this  sub- 
ject, I  believe  it  has  been  found  that  complete  correspondence  of 
averages  is  found  in  the  measurements  of  mankind  only  when  the 
groups  compared  are  sections  of  one  homogeneous  community  thor- 
oughly related  by  community  of  descent.  There  is,  therefore,  reason 
to  believe  that  the  laws  of  heredity  check  divergence  and  secure  uni- 
formity in  proportion  to  free  intermarriage  and  community  of  descent, 
and  that,  if  complete  separation  exists  for  many  generations  between 
two  groups  of  the  same  race,  divergence  will  take  place  though  the 
external  conditions  are  the  same. 

We  therefore  arrive  at  the  conclusion  that,  while  variation  and 
isolation  are  the  essential  factors  in  diversity  of  evolution,  and  inter- 
crossing and  unity  of  descent  the  essential  agents  in  uniformity  of 
evolution,  natural  selection  may  be  an  important  ally  on  either  side. 

II.    Selection  as  an  Explanation  op  Evolution. 

In  discussing  this  subject  we  shall  consider,  i,  What  selection  in 
its  different  forms  does  not  explain;  and  2,  How  far  selection  is  deter- 
mined by  external  nature. 

1,  What  Selection  does  not  Explain. 

(i)  It  can  not  account  for  the  introduction  of  cooperative  and  antici- 
patory action. 

Evidently  it  can  not  account  for  the  powers  on  which  it  depends 
for  its  action.  Now,  natural  selection  presupposes  the  general 
power  possessed  by  every  organism,  of  cooperative  and  anticipatory 
action,  based  upon  a  discrimination  between  the  probable  results  of 
different  actions,  and  directed  toward  the  maintenance  of  that  ideal 
state  in  the  actor  which  we  call  life. 

While  still  in  the  egg  or  attached  to  the  parent,  anticipating  the 
need  of  organs  adapted  to  a  new  environment,  the  organism  builds  in 
different  ways  the  most  wonderful  structures,  all  of  which  are  trans- 
formations of  its  own  simple  colorless  fluid.  This  we  call  growth  and 
development. 

Having  entered  on  independent  life,  it  anticipates  the  tendency  of 
work  and  waste  to  produce  exhaustion,  and  forefends  this  result  by 
appropriating  portions  of  dead,  extraneous  fluid  matter,  transmuting 
it  into  its  own  living  fluids,  from  which  it  rebuilds  the  wasting 
structures.     This  is  assimilation. 

Anticipating  its  need  of  special  substances  to  supply  this  continual 
consumption,  it  executes  many  movements  in  order  to  reach  advan- 


30  THE  EVOLUTION  OV  NATURAL  SPECIES. 

tageous  substances  and  to  avoid  injurious  ones.  This  is  accommo- 
dation. 

Anticipating  the  inevitable  death  that  approaches,  it  produces 
young  of  its  own  kind,  which  shall  perpetuate  the  race.  This  is 
reproduction. 

Anticipating  the  fact  that  external  nature  is  subject  to  change,  and 
that,  even  under  unchanged  conditions,  better  adaptations  are  often 
possible,  it  sends  forth  its  offspring  endowed  with  various  powers,  as 
experiments  in  different  directions,  thus  increasing  the  probability 
that  some  will  survive.     And  this  is  called  variation.* 

Being  thus  wonderfully  endowed,  having  been  placed  in  a  world  in 
which  some  of  the  resources  were  fully  adapted  to  sustain  them,  while 
other  resources  were  only  proximately  available,  and  where  many  of 
the  conditions  were  undergoing  gradual  change — such  beings,  in  such 
a  world,  would  be  constantly  pressing  into  new  spheres  of  existence 
and  adapting  themselves  to  the  changing  world;  for  from  the  very 
nature  of  their  powers  there  would  be  a  greater  propagation  of  those 
better  adapted  and  an  inferior  propagation  of  those  less  adapted  to 
the  various  conditions  into  which  their  segregating  powers  had  driven 
them.  Now,  this  propagation,  according  to  adaptation,  this  survival 
of  the  fittest,  this  selection,  is  the  interaction  of  these  powers  with 
external  nature,  and,  therefore,  can  not  account  for  the  existence  of 
the  powers,  though  their  perfection  may  be  due  to  their  Continuous 
action. 

(2)  Selection  can  not  explain  the  division  of  one  race  into  several 
races. 

Again,  we  see  what  selection  can  not  explain  by  considering  the 
nature  of  the  process.  The  survival  of  the  fittest  results  in  the  breed- 
ing together  of  the  fittest,  and,  therefore,  in  the  increasing  fitness  of 
successive  generations  of  survivors;  but  how  can  it  account  for  the 
division  of  the  survivors  of  one  stock,  occupying  one  country,  into  forms 


*  The  importance  of  anticipatory  action  is  emphasized  by  Benjamin  Kidd  in 
"The  Principles  of  Western  Civilization."  His  term  is  "projected  efficiency." 
The  same  power  is  discussed  by  Prof.  James  Ward,  of  Edinburgh,  under  the  term 
"subjective  (or  hedonic)  selection,  *  *  *  a  teleological  factor  *  *  * 
found  to  belong  to  all  things  living."  (See  Naturalism  and  Agnosticism,  Vol.  I, 
p.  294,  and  Vol.  II,  pp.  92,  161 .)  "Accommodation,"  as  used  by  Prof.  J.  Mark 
Baldwin,  covers  all  acquired  adjustments  of  the  individual  to  the  environment. 
(See  his  Development  and  Evolution.)  Functional  variation  is  used  by  Hertwig 
in  the  same  meaning.  "Acclimatization"  as  used  by  Prof.  Charles  B.  Davenport 
covers  all  forms  of  accommodation  to  unfavorable  conditions.  (See  Experi- 
mental Morphology.) 


SELECTION  AS  AN  EXPLANATION.  3I 

differing  more  and  more  widely  from  each  other?  To  explain  such  a 
result  we  must  find  some  other  law.  I  am  prepared  to  show  that  there  is 
such  a  law  rising  out  of  the  very  nature  of  organic  activities — a  law  of 
segregation — bringing  together  those  similarly  endowed  and  separating 
them  from  those  differently  endowed. 

(3)  Selection  does  not  explain  the  establishing  of  unnecessary  char- 
acters. 

Again,  selection  can  not  explain  the  divergent  transformation  of 
forms  distinguished  from  each  other  in  qualities  that  are  not  related 
to  their  success  in  gaining  a  living  and  propagating  their  kind.  As 
illustrations  of  such  transformation  may  be  mentioned  beautiful 
arrangements  of  color  that  can  not  be  attributed  either  to  natural 
selection  or  to  sexual  selection ;  for  example,  the  patterns  with  which 
many  Hawaiian  snails  are  ornamented,  which  can  not  be  of  use  either 
in  attracting  mates  or  in  gaining  a  living. 

2.  Selection — How  far  Determitied  by  External  Nature. 

Passing  to  the  next  point,  we  inquire  whether  change  in  the  char- 
acter of  the  selection  affecting  any  organism  is  wholly  determined  by 
change  in  external  nature?  Or  can  change  in  the  character  of  the 
selection  be  initiated  and  maintained  through  change  in  the  organism, 
without  any  change  in  the  environment? 

(i)  Herbert  Spencer's  view. — Spencer  distinctly  affirms  that  the  latter 
method  of  change  is  impossible.  The  following  are  his  words :  "That 
there  may  be  continuous  changes  in  organism,  there  must  be  continu- 
ous changes  in  incident  forces."  And,  again,  "At  first,  changes  in  the 
amounts  and  combinations  of  external  inorganic  forces,  astronomic, 
geologic,  and  meteorologic,  were  the  only  causes  of  the  successive 
changes  undergone  by  organisms.  [In  time,  however,]  the  actions 
of  organisms  on  one  another  became  new  sources  of  organic  modifica- 
tions."    (Principles  of  Biology,  sees.  169,  170.) 

Spencer  rests  his  denial  of  the  freedom  of  the  human  will  on  the 
assumption  that  all  vital  activities  are  predetermined  by  activities  in 
the  environment.*  It  is  evident  that  if  our  natural  powers  and  our 
present  conditions  are  so  determined  by  the  environment  that  we 
can  produce  but  one  set  of  actions,  then  no  effort  on  our  part,  either 
individual  or  collective,  can  in  the  least  affect  the  result ;  for  we  can 
not  change  our  circumstances  without  acting,  and  our  actions  are 
already  determined  by  our  circumstances. 


*  See  Principles  of  Psychology,  sec.  220. 


32  THE  EVOLUTION  OF  NATURAL,  SPECIES. 

(2)  External  nature  furnishes  the  means  and  occasions,  but  not  the 
cause. 

But  to  return  to  our  question,  can  anything  be  surer  than  that 
through  the  activities  of  the  organism  changes  in  its  relation  to  the 
environment  are  often  produced ;  and  that  through  these  changes  the 
character  of  its  success  is  changed,  and  so  the  character  of  its  selection.* 
As  we  have  already  observed,  it  is  by  virtue  of  its  power  to  strive  for 
the  continuation  of  its  life  that  an  organism  is  an  organism ;  and  selec- 
tion is  the  direct  result  of  varying  degrees  of  survival  in  the  exercise  of 
this  power.  We  see,  therefore,  that  the  doctrine,  common  among  a 
certain  class  of  evolutionists,  that  the  environment  makes  the  organ- 
ism, rests  on  a  false  assumption,  the  introduction  and  perpetuation  of 
which  has  been  favored  by  the  ambiguities  covered  by  the  phrases  in 
use.  External  nature  can  never  furnish  more  than  the  means,  occasions, 
or  opportunities  for  vital  phenomena.  The  power  to  use  these  means 
in  maintaining  life  lies  wholly  with  the  organism,  and  the  degrees  of 
success  which  it  achieves  are  produced  by  this  power,  and  not  by  the 
environment.  So  far  as  the  environment  consists  of  organisms,  each 
species  of  this  organic  environment  is  working  for  its  own  survival, 
and  not  for  the  survival  of  any  other  species  to  which  it  stands  in  the 
relation  of  environment.  The  bees  take  honey  from  the  flowers  for  the 
preservation  of  themselves  and  their  kindred ;  and  the  flowers  make 
the  bees  distribute  their  pollen,  thus  securing  more  vigorous  seed 
than  could  be  gained  by  self-fertilization;  each  species  working  for 
its  own  preservation  and  perpetuation. 

Another  cause  of  confusion  has  been  the  habit  of  speaking  of  the 
transforming  power  of  selection  as  if  it  were  a  special  power,  or  form 
of  power  quite  distinct  from  the  power  of  variation;  whereas,  it  is 
only  one  of  the  laws  expressing  the  relations  that  exist  between  the 
different  results  of  organic  activity.  Selection  is  the  superior  propa- 
gation of  adapted  forms,  through  the  dependence  of  the  degrees  of 
propagation  on  the  degrees  of  adaptation  produced  by  variation. 
Every  variation  of  the  organism  may  be  regarded  as  more  or  less 
adapted,  and  the  survival  of  each,  according  to  its  degree  of'  adapta- 
tion to  the  natural  environment  surrounding  the  group,  is  natural 
selection ;  but  this  diversity  of  survival  is  the  direct  result  of  the 
varying  adaptation  of  the  organism.  The  transforming  power  of 
natural  selection  is,  therefore,  not  a  different  power  from  variation, 
but  it  is  rather  a  direct  result  of  variation. 


*  See  the  description  of  active  or  endonomic  selection  given  in  Appendix  II, 
and  of  other  forms  of  autonomic  selection  in  Chapters  V-VIII. 


SELECTION  AS  AN  EXPLANATION.  33 

(3)  Change  of  sdcclion  without  change  in  the  environment. 

Darwin's  language  in  describing  the  relation  of  these  different  fac- 
tors has  been  shaped  by  the  relation  in  which  man  stands  to  the  ani- 
mals he  selects  for  breeding.  Here  we  speak  of  the  selecting  power 
as  being  in  the  man  who  determines  what  animals  shall  survive  and 
breed,  and  the  power  of  variation  as  being  in  the  organism  which  fur- 
nished the  varieties  for  his  selection.  But  in  nature  there  is  no  power 
standing  outside  of  the  organism  and  determining  what  kinds  shall 
propagate.  Any  kind,  and  every  kind,  that  can  hit  on  any  means 
of  support  will  survive  and  have  the  opportunity  to  propagate. 
The  means  and  methods  of  survival  are  often  very  various,  and  nature 
shows  no  preference  for  one  method  above  another.  It  is  only 
through  the  different  degrees  of  survival  that  there  comes  to  be  any 
selection,  and  these  degrees  of  survival  depend  on  the  different  powers 
presented  by  the  different  varieties  of  the  organism. 

If  we  wish  to  draw  a  true  parallel  between  natural  selection  and 
rational  selection,  we  must  consider  both  wild  and  domestic  creatures 
as  gaining  opportunity  for  propagation  by  adapting  themselves  to 
the  environment;  the  one  class  varying  so  as  to  be  the  best  able 
to  perpetuate  its  kind  in  the  struggle  for  life  among  irrational 
creatures,  and  the  other  class  by  varying  so  as  to  be  the  most  pleasing 
to  man,  and  through  his  care  and  protection  gaining  a  chance  to  live 
and  propagate.  The  one  class  adapt  themselves  to  the  natural 
environment,  the  other  class  to  the  rational  environment.  From 
this  point  of  view  we  see  that  in  both  classes  propagation  depends  on 
adaptation,  and  that  adaptation  depends  on  variation;  and  this 
dependence  is  selection.  We  must,  therefore,  conclude  that  change  in 
the  character  of  the  selection  may  be  initiated  and  continued  through 
change  in  the  organism  without  any  change  in  the  environment,  except 
what  is  produced  by  the  action  of  the  organism. 

(4)  Diversity  of  selection  due  to  power  of  varied  adaptation. 

In  more  general  terms,  the  relations  of  the  organism  to  the  environ- 
ment are  determined  by  the  power  of  the  organism  to  use  the  environ- 
ment; this  power  of  use  being  defined  as  the  power  of  varied  and 
discriminative  action  with  reference  to  the  maintenance  of  life 
through  the  subordination  of  present  means  to  future  ends.  This 
power  is  found  in  every  living  organism,  but  never  in  the  inor- 
ganic world.  We  can  not  conceive  of  a  living  organism  entirely 
destitute  of  the  power  of  adaptive  and  discriminative  action;  for 
this  is  the  fundamental  distinction  between  the  living  and  the  non- 
living. Nor  can  we  conceive  of  the  prolonged  existence,  in  such  a 
world  as  this,  of  any  organism  entirely  destitute  of  the  power  of 


34  THE  EVOLUTION  OF  NATURAL  SPECIES. 

variation,  for  every  individual  of  such  a  species  would  be  exactly  like 
every  other;  and  there  could  be  no  progressive  adaptation  of  its 
powers  to  the  changing  environment,  through  natural  selection  or 
any  other  process. 

(5)  Must  distinguish  between  the  cause  and  the  conditions  of  evolution! 

In  view  of  these  several  conditions,  we  may  safely  attribute  selec- 
tion and  the  other  laws  of  evolution  resulting  from  adaptive  action 
to  the  organism  as  their  cause,  though  we  know  that  the  environment 
furnishes  the  sum  of  the  conditions,  under  some  combination  of 
which  the  cause  must  act. 

(6)  Statistical  proof  of  natural  selection. 

H.  M.  Vernon,  in  his  Variation  in  Animals  and  Plants,  1903,  pp. 
341-345,  gives  statistical  proof,  quoted  from  Dr.  Bumpus,*  that  the 
English  sparrow  in  the  Northern  States  of  America,  when  suffering 
from  heavy  storms  of  rain,  snow,  and  sleet,  loses  by  death  more  of 
those  presenting  certain  characters  than  of  others.  The  conclusion 
which  Bumpus  draws  is  that  "Natural  selection  is  most  destructive 
of  those  birds  which  have  departed  from  the  ideal  type,  and  its 
activity  raises  the  general  standard  of  excellence  by  favoring  those 
birds  which  approach  the  structural  ideal."  Vernon  shows  from  the 
figures  given  by  Bumpus  that  though  the  longest  and  shortest  birds 
are  most  exposed  to  death  from  such  a  storm,  the  average  length  of 
the  birds  that  recovered  from  the  effects  of  the  storm  after  being 
captured  was  1.27  per  cent  less  than  that  of  the  birds  that  perished. 
The  average  weight  of  those  that  recovered  was  2.38  per  cent,  less 
than  that  of  those  that  perished.  If  these  averages  represent  blasto- 
genic  (or  inherited)  characters  it  would  seem  that  the  species  is  under- 
going transformation  through  exposure  to  a  climate  to  which  it  is 
not  yet  fully  adjusted. 

III.    Discontinuity  of  Species. 

In  his  volume  entitled  "Material  for  the  Study  of  Variation,"  pub- 
lished in  1884,  Bateson  points  to  the  lack  of  correspondence  between 
the  diversity  of  physical  environments  and  the  diversity  of  specific 
forms  as  a  feature  unexplained  by  the  theories  of  either  Lamarck  or 
Darwin.     On  page  5  of  his  book  we  read : 

According  to  both  theories  [the  Lamarckian  and  the  Darwinian]  specific  diver- 
sity of  form  is  consequent  upon  diversity  of  environment,  and  diversity  of  environ- 
ment is  thus  the  ultimate  measure  of  diversity  of  specific  form.  Here,  then,  we 
meet  the  difficulty  that  diverse  environments  often  shade  into  each  other  insen- 
sibly and  form  a  continuous  series,  whereas  the  specific  forms  of  life  which  are 

♦  See  Biol.  Lectures,  Wood's  Hole,  1898,  p.  211. 


DISCONTINUITY  OF  SPECIES.  35 

subject  to  them  on  the  whole  form  a  discontinuous  series.  *  *  *  Tempera- 
ture, altitude,  depth  of  water,  salinity,  in  fact  most  of  the  elements  which  make 
up  the  physical  environment  are  continuous  in  their  gradations,  while  as  a  rule 
the  forms  of  life  are  discontinuous.  Besides  this,  forms  which  are  apparently 
Identical  live  under  conditions  which  are  apparently  very  different,  while  species, 
which  though  closely  allied  are  constantly  distinct,  are  found  under  conditions 
which  are  apparently  the  same. 

He  suggests  that  the  explanation  of  this  lack  of  correspondence 
must  be  sought  in  the  organic  group,  and  not  in  its  environment ;  and 
that  in  the  study  of  variation  is  the  chief  hope  though  even  that  may- 
fail  (p.  17). 

I  entirely  agree  with  Mr.  Bateson  in  regard  to  the  importance  of 
variation  and  of  the  factors  in  the  species  that  control  variation;  and 
prominent  among  these  factors  I  find  either  the  power  of  free  com- 
munication and  intergeneration  or  the  lack  of  this  power.  When  a 
species  possessing  very  limited  powers  for  migrating  and  very  rare 
opportunities  for  transportation  is  surrounded  by  a  mass  of  species 
having  the  usual  powers  and  opportunities,  the  natural  result  is  that 
many  colonies  from  the  species  having  very  limited  powers  become 
completely  isolated  from  each  other  and  from  the  original  stock, 
while  the  surrounding  species  of  plants  and  animals  are  not  isolated 
from  the  groups  of  the  same  species  in  other  places.  A  further  result 
is  that  the  isolated  colonies  become  divergent,  while  the  species  hav- 
ing powers  that  prevent  isolation  remain  the  same  as  in  the  original 
home.  The  isolated  groups  being  prevented  from  crossing  with  each 
other,  there  is  nothing  to  prevent  each  group  from  establishing  its 
own  special  methods  of  dealing  with  the  environment,  and  thus  sub- 
jecting itself  to  special  forms  of  selection,  though  dealing  with  the 
same  environment.  No  better  examples  can  be  found  of  the  diver- 
gence of  isolated  groups  while  exposed  to  the  same  environment  than 
those  presented  by  the  arboreal  snails  of  the  Hawaiian  Islands  and  of 
some  other  regions. 

The  probabilities  are  completely  reversed  in  the  case  of  a  species 
possessing  unusual  powers  for  migrating,  or  extraordinary  opportu- 
nities for  transportation.  For  it  often  happens  that  groups  of  such  a 
species,  occupying  districts  very  unlike,  not  only  in  climate  but  in  the 
prevalent  species  of  plants  and  animals,  will  maintain  free  communi- 
cation and  intergeneration  with  each  other,  and  thus  be  kept  to 
essentially  one  type.  Good  examples  of  unity  of  type  maintained 
notwithstanding  long  exposure  to  diverse  conditions  are  found  in  the 
case  of  certain  species  of  birds  and  insects  possessing  great  powers  of 
flight. 


36  THE  EVOLUTION  OF  NATURAL  SPECIES. 

The  principle  underlying  both  classes  of  cases  is  that  free  intergen- 
eration  insures  unity  of  type,  and  that  the  prevention  of  free  com- 
munication and  of  free  crossing  prevents  the  operation  of  reflexive 
selection*  between  the  isolated  groups,  and  also  opens  the  way  for 
diversity  in  the  use  of  the  environment,  and  so  leads  to  diversity  in 
other  forms  of  selection.  Isolation,  therefore,  cooperating  with  the 
power  of  variation  and  with  the  principle  of  selection  of  other  forms 
than  natural  selection,  goes  far  toward  explaining  the  phenomena 
which  we  have  been  considering,  and  which  are  essentially  the 
same  as  those  which  Mr.  Bateson  has  cited  as  being  in  pressing  need 
of  explanation.  Discontinuous  variation  explains  the  lack  of  inter- 
mediate forms  in  certain  cases,  but  it  is  not  the  necessary  explanation 
in  every  case. 

The  related  subject  of  mutation  is  briefly  considered  in  Chapter  V, 
at  the  end  of  section  III.  Those  interested  in  the  subject  of  the  dis- 
continuity of  closely  related  species  will  find  an  interesting  summary 
of  the  facts  and  interpretations  in  "The  Method  of  Evolution,"  by 
Professor  Conn,  pages  35,  115  to  139,  359. 


*  Reflexive  selection  is  described  in  Appendix  II,  I,  8,  (3),  as  "depending  on 
the  relations  of  the  members  of  a  species  to  .each  other."  The  most  famil- 
iar forms  of  reflexive  selection  are  sexual  and  social  selection.  It  is,  of  course, 
manifest  to  every  one  that  two  completely  separated  groups  of  the  same  species 
can  have  no  influence  over  each  other  through  sexual  and  social  selection.  Other 
forms  of  reflexive  selection  are  considered  in  Chapter  VI ;  also  the  fact  that  there 
are  endonomic  forms  of  environal  selection. 


CHAPTER  IV. 

DIVERGENCE  UNDER  THE  SAME  ENVIRONMENT. 

Explanation  of  Plate  I. 

Plate  I  presents  2 1  species  of  8  genera  of  one  family  found  on  five  of 
the  islands  of  the  Hawaiian  group.  These  islands  are  within  sight  of 
each  other,  having  the  same  climate  and  much  the  same  vegetation, 
and  (with  the  exception  of  the  different  forms  of  snails)  the  same  spe- 
cies of  animal  life ;  and  yet  how  great  the  diversity  presented  by  the 
species  of  the  same  genus,  not  to  mention  the  greater  divergence 
attained  by  the  different  genera.  These  eight  genera,  and  the  two 
genera  represented  in  Plates  II  and  III,  all  belong  to  the  family  of 
Achatinellidae,  found  in  no  part  of  the  world  outside  of  the  Hawaiian 
Islands.  These  genera,  though  differing  widely  in  form  and  habits, 
have  one  shell-characteristic  which  does  not  occur  in  the  same  degree 
in  snail  shells  found  in  other  parts  of  the  world.  It  will  be  observed 
that  the  small  glassy  genus  Leptachatina  (fig.  5),  and  the  minute  Auri- 
culella,  with  a  sharp  plate  in  the  aperture  (fig.  3),  are  like  the  much 
larger  shells  of  the  other  genera,  in  that  they  have  a  twist  in  the  colu- 
mella. The  character  appears  in  a  greater  or  less  degree  in  all  the  ten 
genera  by  which  the  Achatinellidae  are  represented. 

Of  these  eight  genera,  Carelia  is  found  only  on  Kauai,  Apex  and 
Bulimella  only  on  Oahu,  while  Amastra  (and  probably  Leplachatina), 
is  found  on  all  the  isxands  of  the  group,  and  Auriculella,  Ivaminella, 
and  Partulina  are  found  on  the  central  islands,  that  is,  on  Oahu,  Molo- 
kai,  Landi,  and  Maui.  The  one  arboreal  species  I  have  received  from 
the  island  of  Hawaii  is  either  a  Partulina  or  a  Newcombia,  the  specific 
name  being  physa  (Newcomb) .  The  typical  forms  of  Newcombia  are 
found  on  Maui  and  Molokai.  Laminella  and  Partulina  find  special 
development  on  Maui,  Molokai,  and  Lanai,  where  they  are  represented 
by  many  species.  The  genera  most  characteristic  of  the  island  of  Oahu 
are  Bulimella,  Achatinella,  and  Apex.  The  most  nearly  allied  species 
from  different  islands  do  not  completely  intergrade  as  do  those  from 
the  same  island.  For  example,  Partulina  splendida  of  Maui  (fig.  14) 
does  not  completely  intergrade  with  P.  virigulata  of  Molokai  (fig.  12)^ 
or  with  P.  -variabilis  of  Lanai  (fig.  13),  as  it  does  with  certain  other  spe- 
cies of  Partulina  found  on  Maui.  The  species  of  this  genus  have  been 
so  chosen  as  to  present  from  each  island  the  form  most  nearly  related 
to  Partulina  splendida.     So  also  in  the  case  of  the  Laminella,  it  is  not 

37 


38  DIVERGENCE    UNDER   THE    SAME   ENVIRONMENT. 

the  most  divergent  species  that  have  been  chosen,  but  the  most  closely- 
related  of  those  found  on  the  different  islands. 

In  the  case  of  arboreal  species,  the  isolation  between  those  inhab- 
iting the  forests  of  East  Maui  and  those  inhabiting  the  forest  of 
West  Maui  is  almost  as  complete  as  if  they  inhabited  separate  islands ; 
for  the  open  grass  land  separating  the  two  masses  of  forest-covered 
mountains  is  as  complete  a  barrier  against  direct  migration  as  would 
be  a  salt-water  channel.  There  is,  however,  a  somewhat  better 
chance  of  transportation  by  human  agency  across  grass  land  than 
across  an  equal  width  of  water. 

Carelia  is  always  dextral  in  form ;  and  I  think  it  is  terrestrial  in  its 
habits.  Amastra  and  Leptachatina,  which  are  almost  always  found 
on  the  ground,  are  with  extremely  rare  exceptions  dextral  in  form; 
while  of  the  arboreal  genera,  Newcombia  and  Laminella  are  almost 
always  sinistral,  and  Auriculella,  Apex,  and  Partulina  have  some  spe- 
cies constantly  sinistral,  others  constantly  dextral,  and  others  that 
assume  either  form.  Achatinella  and  Bulimella  (represented  in  Plates 
II  and  III),  are  constantly  arboreal  in  habits,  and  both  dextral  and 
sinistral  in  the  forms  assumed. 

The  following  abbreviations  are  used  in  the  "Notes"  on  the  species 
given  in  Plates  I,  II,  and  III. 

Fer.  =  Ferussac;  Gk.  =  Gulick;  Migh.  =  Mighels;  Nwc.  =  Newcomb;  Pfr.  = 
Pfeiffer;  Rv.  =  Reeve;  Sm.  =  Smith;  Swn.  =  Swainson;  D  =  dextral  in  form; 
S  =  sinistral  in  form;  D  >  S  ^=  the  majority  are  dextral;  S  >  D  =  the  majority 

are  sinistral ;  S  —  D  -— -  =  sinistral  with  the  exception  of  about  i  in  5CX). 

NOTES  ON  THE  SPECIES. 

Fig.  I.  Carelia  cocklea  (Rv.)  D.  From  the  island  of  Kauai.  Examination  of 
the  organs  will  probably  place  it  with  the  Achatinellidse. 

Fig.  2.   Amastra  nucleola  (Gould)  D.     From  Waiole,  Kauai. 

Fig.  3.  Auriculella  auricula  (Fer.)  D  >  S.  This  species,  like  others  of  this 
genus,  is  found  on  the  leaves  of  trees  and  shrubs.  Its  habitat  is  the  eastern  por- 
tion of  the  forest  region  of  the  island  of  Oahu  This  specimen  is  from  the  valley 
of  Palolo. 

Fig.  4.  Apex  apicatus  (Nwc.)  D  >  vS.  From  Wahiawa,  Oahu.  Also  found  in 
Helemano  and  Ahonui. 

Fig.  5.  Leptachatina  fumosa  (Nwc.)  D.  Found  on  the  ground  under  dead 
leaves,  in  damp  forest  regions  from  Nuuanu  to  Palolo,  on  the  island  of  Oahu.  This 
specimen  is  from  Palolo. 

Fig.  6.  Laminella  sanguinea  (Nwc.)'  S.  Found  in  Helemano  and  Wahiawa  and 
the  intervening  regions  on  the  island  of  Oahu.     This  specimen  is  from  Helemano. 

Fig.  7.  Laminella  citrina  (Migh.)  S.     From  the  island  of  Molokai. 

Fig.  8.  Laminella  tetrao  (Nwc.)  S.     From  the  island  of  Lanai. 

Fig.  9.  Laminella  venusta  (Migh.)  S.     From  Lahaina,  West  Maui. 

Fig.  10.  Laminella  bulbosa  (Gk.)  S.     From  Kula,  East  Maui. 

Fig.  ii.  Partulina  dubia  (Nwc.)  D.  This  is  a  rare  species  distributed  over  a 
number  of  valleys  of  the  island  of  Oahu  from  Waianae  to  Kalihi.     This  specimen 


EXPLANATION   OF   PLATE    II.  39 

is  probably  from  Kalihi.  No  other  species  from  the  Hawaiian  Islands  seems  to 
so  closely  resemble  the  Partula  found  on  many  of  the  islands  of  the  Pacific.  Still 
it  must  belong  to  the  Achatinellidae,  for  it  completely  intergrades  with  Partulina 
densilineata,  which  presents  the  peculiar  twist  of  the  columella,  the  most  constant 
shell-character  of  the  Hawaiian  family  of  snails.* 

Fig.  12.   Partulina  virigulata  (Nwc.)  D  >  S.     From  the  island  of  Molokai. 

Fig.  13.  Partulina  variabilis  (Nwc.)  S.     From  the  island  of  Lanai. 

Fig.  14.  Partulina  splendida  (Nwc.)  D  >  S.     From  Lahaina,  West  Maui. 

Fig.  15.  Partulina  plumbea  (Gk.)  D.  From  Kula,  East  Maui;  found  on  the 
trunks  of  trees  several  thousand  feet  above  the  sea  level. 

Fig.  16.  Newcombia  cumingii  (Nwc.)  S.     From  Makawao,  East  Maui. 

Fig.  17.  Amastra  turritella  (Fer.)  D.  Found  on  dead  trees  from  Waiawa  east- 
ward to  Keawaawa,  island  of  Oahu.     This  specimen  is  from  Palolo. 

Fig.  18.   Amastra  violacea  (Nwc.)  D.     From  the  island  of  Molokai. 

Fig.  19.  Awa^/ra  wmg/ia  (Adams)  D.     From  the  island  of  Lanai. 

Fig.  20.  Amastra  mastersi  (Nwc.)  D.     From  Lahina,  West  Maui. 

Fig.  21.  Amastra  nigra  (Nwc.)  D.     From  Kula,  East  Maui. 

The  Darwinian  theory  explains  the  unity  of  form  in  the  different 
genera  and  species  of  one  family  by  the  theory  that  they  are  all  de- 
scended from  one  original  intergenerating  stock.  The  diversity  in  the 
forms  is  explained  as  the  result  of  variation,  with  diversity  in  the  forms 
of  selection  produced  by  exposure  to  different  environments.  In  explain- 
ing the  divergence  in  the  genera  of  this  family,  I  think,  we  shall  come 
nearer  to  the  facts  if  we  attribute  the  diversity  in  the  selection,  to 
which  they  have  been  exposed  for  countless  generations,  to  diversity 
in  the  methods  of  using  the  environment  adopted  by  completely  isolated 
groups.  The  divergence  in  many  of  the  closely  related  species,  found 
on  the  same  species  of  trees  in  successive  valleys  on  the  same  moun- 
tain range,  is,  I  think,  due  to  isolation  and  variation,  without  any  differ- 
ence in  the  forms  of  selection. 

Explanation  of  Plate  II. 

This  plate  presents  25  species  of  Achatinella,  a  genus  of  arboreal 
snails  found  on  the  island  of  Oahu,  and  most  of  them  confined  to  dis- 
tricts from  I  to  3  or  4  miles  in  extent.  Achatinella  is  one  of  ten  genera 
of  the  Achatinellidae,  of  which  there  are  between  200  and  300  species 
and  over  a  thousand  varieties,  on  this  island  only  40  miles  long. 
Eight  of  these  genera  are  given  on  Plate  I,  and  one  on  Plate  III.  This 
plate  illustrates  the  relationship  of  species  distributed  in  different 
valleys  on  the  same  island.  The  letter  attached  to  each  figure  desig- 
nates the  valley  or  small  district  in  which  the  specimen  figured  was 
found.     The  position  of  this  valley  or  district  on  the  island  is  easily 


*  A  careful  comparison  of  the  internal  structure  of  this  species  with  the  struc- 
ture of  the  Partula  of  the  South  Pacific  might  perhaps  reveal  points  of  special 
interest  in  the  relations  of  the  two  groups. 


40  DIVERGENCE    UNDER   THE    SAME   ENVIRONMENT. 

discovered  by  reference  to  the  map  of  Oahu  preceding  Plate  II,  where 
the  same  letters  are  used  to  designate  positions.  It  will  be  observed 
that  underscored  letters  are  used  to  designate  positions  on  the  north- 
east side  of  the  main  mountain  range,  and  that  Roman  letters  are  used 
to  designate  the  positions  on  the  southwest  side  of  the  same  range. 
These  are  so  arranged  that  the  valleys  indicated  by  the  two  forms  of 
any  one  letter  are  nearly  opposite  to  each  other. 

The  twenty-five  species  presented  in  this  plate  would  have  to  be 
considered  as  one  species  if  we  accepted  the  statement  that  the  find- 
ing of  completely  intergrading  forms  between  two  types  proves  that 
they  are  varieties  of  the  same  species.  If,  on  the  other  hand,  we 
adopt  the  statistical  method  of  testing  species,*  these,  and  many  more 
fourid  in  the  forests  of  the  same  mountain  range,  will  have  to  be  classed 
as  species.  The  collection  of  the  species  and  varieties  of  this  genus, 
made  by  me  from  1850-to  1852,  present  a  complete  series  of  intergra- 
dations  between  the  larger  forms  found  on  the  trunks  of  the  candle- 
nut  tree  in  the  eastern  valleys  of  Oahu,  and  the  small  forms  found  on 
the  leaves  of  the  lobelia  and  other  shrubs  in  the  western  valleys  of  the 
island,  where  groves  of  the  candle-nut  tree  abound,  occupied  more  or 
less  by  species  of  Bulimella,  but  neglected  by  the  representatives  of 
the  genus  Achatinella.  As  no  one  will  maintain  that  these  most  diver- 
gent types  of  the  genus  belong  to  the  same  species,  the  existence  of 
such  a  series  of  intergrading  links  becomes  a  strong  argument  for  the 
belief  that  divergent  forms  properly  ranking  as  species  have  arisen 
from  one  original  species,  through  the  cumulative  effects  of  variation 
cooperating  with  a  series  of  isolations,  each  isolation  lasting  for  many 
generations  before  the  next  occurs. 

The  genera  most  characteristic  of  Oahu  are  Achatinella,  Bulimella, 
and  Apex;  for,  with  the  exception  of  two  or  three  species  of  Achati- 
nella found  on  the  island  of  Molokai,  they  are  limited  in  their  distribu- 
tion to  this  island.  Their  distribution  in  the  different  districts  of  the 
island  is  probably  due  to  the  adaptation  of  Bulimella  to  a  damp  cli- 
mate, and  of  Achatinella  to  a  region  of  dense  shade,  but  of  less  rain, 
and  of  Apex  to  a  comparatively  dry  climate.  As  regards  rainfall,  the 
northeast  side  of  the  main  range  catches  the  trade  winds  as  they  come 
from  the  ocean,  and  receives  the  heaviest  fall ;  on  the  southwest  side 
of  the  same  range  there  is  less  rain ;  and  on  the  shorter  range,  on  the 
southwest  side  of  the  island,  there  is  still  less  rain.  In  the  first  region 
we  find  Bulimella  and  a  very  few  Achatinella;   in  the  second  region 


*  The  explanation  of  Plate  III  brings  out  the  fact  that  the  individuals  represent- 
ing intermediate  forms  are  very  rare  compared  with  those  of  typical  forms.  Such 
species  meet  the  statistical  test. 


EXPLANATION   OF   PLATE   III.  4I 

both  Bulimella  and  Achatinella  in  the  shady  valleys,  with-  Apex  on 
the  comparatively  sunny  ridges;  and  in  the  third,  several  abundant 
species  of  Apex,  and  but  one  species  of  Bulimella,  and  but  one  of  Acha- 
tinella, both  of  these  being  extremely  rare. 

NOTES  ON  THE  SPECIES. 
Fio.  I.   Achatinella  zonula  (Gk.)  S.     From  Pupukea. 
Fig.  2.  Achatinella  albescens  (Gk.)  S.     From  Pupukea. 
Fig.  3.  Achatinella  recta  (Nwc.)  S.     From  Kawailoa. 
Fig.  4.   Achatinella  herbacea  (Gk.)  S.     From  Kawailoa. 
Fig.  5.  Achatinella  delta  (Gk.)  S.     From  Wahiawa. 
Fig.  6.  Achatinella  rhodorhaphe  (Sm.)  S.     From  Wahiawa. 
Fig.  7.  Achatinella  pygmcea  (Sm.)  S.     From  Ewa. 
Fig.  8.  Achatinella  ligata  (Sm.)  D.     From  Ewa. 
Fig.  9.  Achatinella  analoga  (Gk.)  S.     From  Halawa. 
Fig.  10.  Achatinella  colorata  (Rv.)  S.     From  Halawa. 
Fig.  1 1.   Achatinella  adusta  (Rv.)  S.     From  Pauoa. 
Fig.  12.   Acltatinellacastanea  (Rv.)  S.     From  Pauoa. 
Fig.  13.  Achatinella  olivacea  (Kv.)  S.     From  Pauoa. 
Fig.  14.   Achatinella  dunkeri  {Cuming)  S.     From  Makiki. 
Fig.  15.   Achatinella  producta  (Rv.)  D  >  S.     From  Makiki. 
Fig.  16.   Achatinella  buddii  (Kwc.)  S.     From  Makiki. 
Fig.  17.   Achatinella  johnsonii  (Nwc.)  S  >  D.     From  Manoa. 
Fig.  18.   Achatinella  stewartii  {QiT^en)  Ti  ^  S.     From  Manoa. 
Fig.  19.   Achatinella  fuscozona  (Sm.)  S.     From  Manoa. 
Fig.  20.   Achatinella  trilineata  (Gk.)  S.     From  Palolo. 

Fig.  2 1 .  Achatinella  varia  (Gk.)  S  —  D  -— .     From  Palolo. 

Fig.  22.   Achatinella  bacca  (Rv.)  D.     From  Palolo. 
Fig.  23.  Achatinella  plumata  (Gk.)  S.     From  Waialae. 
Fig.  24.  Achatinella  diversa  (Gk.)  S.     From  Waialae. 
Fig.  25.   Achatinella  abbreviata  (Rv.)  D.     From  Waialae. 

Explanation  of  Plate  III. 
The  purpose  of  this  plate  is  to  illustrate  the  variations  and  inter- 
grading  forms  of  closely  related  species  of  the  Achatinellidge.  The  25 
shells  figured  in  this  plate  are  found  in  the  northwestern  portion  of  the 
island  of  Oahu,  and  are  regarded  as  belonging  to  four  species,  of  which 
Bulimella  ovata  Nwc.  is  presented  under  ten  variations,  five  being  of 
the  dextral  form  (see  figs.  6  to  10),  and  five  of  the  sinistral  form  (see 
figs.  II  to  15).  Of  these  figure  10  is  found  in  Hakepuu,  and  the  rest 
in  Kahana.  Figures  i  to  5  are  of  Bulimella  hulimoides  Swn.,  found  in 
Kawailoa;  figures  16  to  20  are  of  Bulimella  obliqua  Gk.,  found  in 
Kahana ;  figures  2 1  to  25  are  of  Bulimella  rosea  Swn.,  of  which  figures 
21  to  24  are  found  in  Wahiawa,  and  figure  25  is  found  in  Helemano. 
Intergrading  forms  are  found  between  figure  5  of  this  plate  and  Buli- 
mella glabra  Nwc. ;  between  figure  8  of  this  plate  and  Bulimella  oomor- 
pha  Gk. ;  between  figure  1 5  of  this  plate  and  Bulimella  rotunda  Gk. 


42  DIVERGENCE    UNDER   THE   SAME    ENVIRONMENT. 

The  relative  numbers  in  which  these  different  variations  occur  are 
roughly  indicated  in  the  following  table,  in  which  the  numbers  not 
inclosed  in  parentheses  correspond  with  the  figures  in  Plate  III,  while 
the  number  in  parentheses  below  each  one  of  these  indicates  approxi- 
mately the  relative  frequency  in  which  it  was  found. 

I  2  3456  78  9  10  II  12  13 

(200)     (150)     (100)    (60)     (30)     (2CX))     (200)    (200)     (200)     (100)    (200)    (200)     (200) 


14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

(100) 

(60) 

(1) 

(200) 

(200) 

(200) 

(60) 

(30) 

(300) 

(45) 

(15) 

(15) 

The  metropolis  of  Bulimella  rosea  is  Wahiawa,  where  the  most 
abundant  type  of  coloring  is  seen  in  figure  22,  which  is  snowy  white 
with  a  pink  lip.  In  Helemano  district,  the  shells  of  this  species  are 
somewhat  smaller,  with  the  lip  more  frequently  white,  and  the  body 
of  the  shell  not  as  snowy  white  as  is  usually  the  case  in  the  metropolis. 
Figure  2 1  is  a  comparatively  rare  variety  of  B.  rosea,  white  throughout 
and  intergrading  with  B.  ovata  through  a  nearly  white  variety  of  the 
sinistral  form  of  that  species,  occurring  in  Kahana  in  the  proportion  of 
perhaps  one  to  a  thousand  of  the  normal  specimens  of  the  species. 
Again,  in  figure  16,  we  have  a  very  rare  form  connecting  Bulhnella 
ohliqua  with  Bulimella  ovata. 

Oahu  the  Metropolis  of  the  AcH.\TiNELLiniE. 
The  island  of  Oahu  may  be  regarded  as  the  metropolis  of  the  Acha- 
tinellidae,  for  on  this  island  we  find  8  of  the  10  genera,  while  on  Maui 
and  Molokai  together  we  find  7  genera,  and  on  Kauai  3  genera.  Suf- 
ficient attention  has  not  been  given  to  the  land  snails  of  Hawaii  to 
enable  us  to  give  a  full  report ;  but  I  am  told  that  there  is  an  unusual 
development  of  Succinea  on  that  island,  while  the  Achatinellidae  are 
but  very  meagerly  represented.  One  explanation  of  the  small  devel- 
opment on  the  island  of  Hawaii  of  the  family  of  snails  which  is  so 
fully  developed  on  the  island  of  Oahu  is  found  in  volcanic  eruptions, 
which  on  the  island  of  Hawaii  have  from  time  to  time  destroyed  the 
forests  till  recent  years;  while  on  the  island  of  Oahu  it  is  probably 
hundreds  of  thousands  of  years  since  such  complete  destruction  of  the 
necessary  conditions  of  existence  for  these  creatures  has  occurred. 


Plate  A. 


GULICK 


Plate 


Plate  B. 


GULICK 


Plate  II 


Distribution   of  Twenty-five   Species  of   Achatinella 
FROM   Ten   Valleys 


GULICK  p^^_     ,„ 


Variation  and   Intergrading  of  Four   Species  of  Bulimella 


EXPLANATION   OF   PLATE   B. 


43 


Letters  used  on  Plate  B,  to  designate  the  Valleys  and  Districts  on 
THE  Island  of  Oahu. 


a,  Waialei 

b,  Pupukea. 

c,  Waimea. 

d,  Kawailoa. 

e,  Opaiula. 

f,  Helemano. 

g,  Wahiawa. 
h,  Ahonui. 

i,  Kalaikoa. 
j,  Waipio. 
k,  Waiawa. 
1,  Ewa|Waimano. 
l  Waimalu. 
m,  Halawa. 
n,  Moanalua. 

o,   Kalihi. 

p,  Nuuanu. 
q,  Pauoa. 
r,  Makiki. 

s,  Manoa. 
t,  Palolo. 
u,  Waialae. 
V,  Wailupe. 
w,  Niu. 
X.  Keawaawa. 


o,  Kahuku. 

b,  Malaikahana. 

c,  Laie. 

d,  Hauula. 

e,  Kaliuwaa. 
/,  Waiolu. 

g,  Punaluu. 
h,  Kahana. 
i,  Keawa. 
J,  Hakepuu. 
k,  Waikane. 
/,  Waiahole. 


m,  Kaalaea. 
n,  Kahaluu. 

Ahuimanu. 

loleka. 
p,  Kaneohe. 


Heiaj 


(  Olomana  Peak 


/,  u,  V,  w,  Waimanalo. 


M,  Mokuleia. 
L,  Lehui. 
W,  Waianae. 


[Italic  letters  in  the  second  column  are  to  be  regarded  as  the  equivalent  of  the  underscored 
letters  on  the  map.] 


CHAPTER  V. 

THE  FOUR  SEGREGATIVE  PRINCIPLES, 

I.    The  Need  of  a  Nomenclature  Distinguishing  between  Racial  and 
Habitudinal,  Segregation. 

1.  The  Interaction  of  Acquired  and  Inherited  Char  cutters. 

The  interaction  of  the  factors  producing  racial  segregation  and 
those  producing  social  or  habitudinal  segregation  should,  I  think,  be 
clearly  recognized,  and  a  suitable  nomenclature  used  for  presenting 
the  same.  Increasing  attention  is  being  given  to  this  interplay  of 
influences ;  but  clear  expression  of  the  relations  of  the  factors  is  con- 
stantly obscured  by  lack  of  terms  for  designating  the  processes  of 
segregation  relating  to  acquired  characters  or  habitudes. 

In  my  paper  on  "Intensive  Segregation"  I  emphasize  the  impor- 
tance of  the  forms  of  reflexive  selection  "due  to  the  relations  of  the 
members  of  the  same  species  to  each  other,  and  liable  to  change  with- 
out any  change  in  the  environment,"  and  of  active  (or  endonomic) 
selection  "due  to  change  in  the  successful  use  of  the  powers  of  the 
organism  in  dealing  with  the  environment."  In  another  paragraph 
I  say :  ' '  Diversity  in  the  uses  to  which  different  sections  of  one  species 
put  their  powers  when  appropriating  resources  from  the  same  envi- 
ronment must  produce  diversity  in  the  forms  of  variation  that  are 
most  successful  in  the  different  sections.  This  I  call  active  selection 
as  contrasted  with  passive  selection,  which  varies  according  to  differ- 
ences in  the  environment.  All  diversities  of  environal  selection  that 
do  not  vary  according  to  differences  in  the  environment  must  be 
classed  as  diversities  of  active  selection,  for  they  must  have  originated 
in  some  variation  in  the  powers  of  the  organism,  or  in  the  diversity  of 
uses  to  which  it  has  put  its  powers."*  The  power  of  the  organism  to 
determine  industrial  segregation  is  considered  in  my  paper  on  ' '  Diver- 
gent Evolution,"  read  before  the  Linnean  Society  in  1887. 

In  1896,  Professors  Baldwin,  Osborn,  and  Lloyd  Morgan  were  inde- 
pendently led  to  consider  the  influence  of  individual  powers  of  accom- 
modation in  enabling  representatives  of  a  species  to  survive  in  an 
environment  that  would  otherwise  be  fatal,  and  so  "giving  time  to 
the  species  to  develop  coincident  variations  (i.  e.,  congenital  varia- 

*  See  Appendix  II,  Section  I,  8,  (4)  and  (18). 

45 


46  THE   FOUR   SEGREGATIVE   PRINCIPLES. 

tions  in  the  same  direction)/'*  which  are  gradually  accumulated  by 
selection.  Another  point  presented  by  the  same  writers  is  the  conti- 
nuity of  tradition,  secured  by  training,  suggestion,  and  example  on 
the  part  of  the  parents  and  imitation  on  the  part  of  the  young.  The 
effects  of  tradition  have  also  been  very  clearly  illustrated  by  F.  W. 
Headley  in  his  recent  book.f  I  quote  a  few  sentences  in  which  he 
summarizes  the  effects  of  accommodation  and  tradition : 

The  result  is  that  among  the  higher  plastic  classes  of  animals  evolution  proceeds 
more  rapidly.  But  obviously  the  quickening  up  of  evolution  is  not  all.  The 
individual  gains  in  importance.  He  improves  his  powers,  is  able  to  face  a  change 
of  environment  that  otherwise  would  have  been  fatal.  He  makes  an  environment 
for  his  young  in  which  intelligence  can  be  developed ;  he  chooses  the  environment 
which  they  shall  have  when  out  of  the  nursery,  and  so  decides  to  some  extent  what 
qualities  shall  be  the  winning  qualities  in  life.  In  fact,  he  is  beginning  to  take  the 
helm  and  steer  the  species.  Or  we  may  put  it  in  this  way :  When  the  individuals 
of  one  generation  decide  the  environment  in  which  the  next  shall  grow  up,  selec- 
tion ceases  to  be  purely  natural;  it  is  in, part  artificial. J 

These  quotations  are  sufficient  to  show  that  there  is  increasing 
recognition  of  the  fact  that  there  may  be  changes  in  the  organism 
that  are  not  dependent  on  changes  in  the  environment,  and  are  there- 
fore not  dependent  on  change  in  the  form  of  the  natural  selection.  In 
choosing  terms  for  designating  these  processes  I  think  we  should  care- 
fully follow  Professor  Baldwin's  suggestion  "that  selection  in  the 
Darwinian  sense  should  be  used  only  when  the  essential  conditions 
of  organic  progress  by  survival  are  present,  namely,  variations  and 
physical  heredity."? 

In  my  own  usage,  selection  has  been  applied  only  to  processes  secur- 
ing the  survival  of  part  of  the  variations  of  a  race  or  species  with  the 
exclusion  of  other  variations,  and  so  influencing  its  powers  of  heredity ; 
and  isolation  has  been  limited  to  the  prevention  of  free  crossing  be- 
tween co-existing  groups.  In  order  to  do  this,  and  at  the  same  time 
clearly  present  the  principles  controlling  the  evolution  of  habitudes,  it 
has  been  necessary  to  find  two  terms  that  might  hold  the  same  rela- 
tion to  innovation  and  tradition  that  selection  and  isolation  hold  to 
variation  and  heredity.     The  best  words  I  have  found  are  election 


*  See  letter  from  J.  Mark  Baldwin  in  Nature  for  April  15,  1897,  also  the  same  in 
Science  for  April  23,  1897,  on  "Organic  Selection."  In  this  letter  will  be  found 
references  to  discussion  on  the  subject  during  the  previous  year  in  various  books 
and  journals. 

t  Problems  of  Evolution,  pp.  120-128.  London,  Buckworth  &  Co.,  1900,  and 
New  York,  Crowell  &  Co.,  1901. 

I  Problems  of  Evolution,  p.  128. 

§  See  Science  May  8,  1898.  The  same  limitation  is  also  advocated  in  his  Social 
and  Ethical  Interpretations,  Appendix  B. 


SEGREGATION  A  FUNDAMENTAL  LAW  IN  THE  ORGANIC  WORLD.     47 

and  partition.  The  need  of  such  terms  will,  I  am  sure,  be  recognized 
by  many,  though  some  may  not  consider  the  words  I  have  chosen  the 
best. 

2.  Segregation  is  a  Fundamental  Law  in  the  Organic  World. 

One  sphere  in  which  it  operates  is  racial  (or  aptitudinal)  segrega- 
tion, produced  by  the  intergeneration  of  individuals  with  like  innate 
characters.  Another  sphere  is  social  (or  habitudinal)  segregation, 
produced  by  the  association  with  each  other  of  individuals  with  like 
acquired  characters.  Segregate  generation  (i.  e.,  the  generation  of 
like  with  like) ,  is  a  condition  on  which  the  present  structure  of  the  organic 
world  depends.  Without  segregate  generation  the  differences  of 
races,  species,  genera,  and  the  higher  groups  could  never  have  arisen, 
and  if  it  were  possible  that  it  should  cease,  all  these  distinctions 
would  ere  long  be  obliterated.  The  fact  that  race  characters  are 
hereditary  renders  it  certain  that  freely  intergenerating  races  will,  in  a 
few  generations,  become  one  race.  But  the  fundamental  nature  of 
the  organic  world  is  such  that  the  only  cases  in  which  the  law  of  segre- 
gation can  be  broken  down  are  those  in  which  the  divergence  is  com- 
paratively small.  When  amalgamation  takes  place  it  is  usually 
varieties  of  the  same  species  that  unite.  When  physiological  incom- 
patibility has  once  been  fully  established,  the  segregation  is  never 
broken  down ;  but,  on  the  other  hand,  as  long  as  there  is  any  plasticity 
in  a  race,  it  is  possible  that  new  segregations  may  be  introduced  and 
one  race  divided  into  two  or  more  races. 

Having  observed  that  segregate  generation  is  the  fundamental 
principle  by  which  the  world  of  sexually  reproducing  organisms  is 
maintained,  and  having  discovered  that  the  art  of  breeding,  by  which 
the  multitude  of  domestic  races  has  been  produced,  rests  on  the 
control  of  segregate  breeding,  we  propose  to  make  careful  investiga- 
tion of  the  different  forms  of  control  influencing  this  principle  and  of 
the  efifects  thus  produced. 

As  an  equivalent  for  segregate  generation  (or  the  breeding  of  like 
individuals  with  like),  Romanes  has  proposed  the  term  "homogamy." 
An  objection  to  its  use  in  this  meaning  is,  however,  found  in  the  fact 
that  in  botanical  language  the  same  term  has  a  somewhat  different 
meaning. 

It  should  be  noted  that  this  statement  concerning  the  breeding  of 
like  with  like  does  not  imply  that  creatures  freely  mating  with  each 
other  are  entirely  free  from  differences.  Of  multicellular  organisms 
no  two  were  ever  found  to  be  exactly  alike ;  if,  therefore,  there  is  any 
mating  of  these  creatures,  it  must  be  the  mating  of  creatures  that 
are  not  completely  the  same,  either  in  structure  or  function.     The 


48  THE   IfOUR   SEGREGATIVE   PRINCIPLES. 

point  is  that  the  greatest  difference  existing  between  any  form  of 
organisms  and  any  other  form  that  is  capable  of  crossing  with  it,  is 
very  small  compared  with  the  differences  presented  by  the  vast 
world  of  organisms  that  are  incapable  of  crossing  with  it.  Cross- 
fertilization  secures  the  blending  of  elements  from  individuals  that 
are  more  or  less  divergent;  but  the  degree  of  divergence  that  may 
exist  without  resulting  in  sexual  incompatibility,  either  physiological, 
morphological,  or  psychological,  is  very  small  compared  with  the 
divergences  that  lie  beyond  the  limits  of  compatibility.  Again,  we 
find  that  in  some  cases  species  incapable  of  crossing  are  so  similar  in 
visible  characters  that  the  naturalist  finds  difficulty  in  distinguishing 
them. 

3.  Segregate  Association*  a  Fundamental  Law  on  which  the  Social  Structure  of 
Each  Species  titat  is  not  wholly  guided  by  Instinctive  Aptitudes  must  rest. 

The  necessity  of  a  common  language  for  a  social  group  will  be  rec- 
ognized by  all.  There  must  be  a  system  of  signs  or  signals  by  which 
the  members  of  one  group  may  call  to  each  other  when  they  wish  to 
come  together,  may  warn  each  other  of  approaching  danger,  and  may 
in  other  ways  cooperate  in  securing  the  sustenance,  protection,  and 
propagation  of  the  group.  If  these  signs  are  not  instinctively  made 
and  instinctively  understood,  they  must  depend  on  suggestion,  train- 
ing, and  imitation;  and  this  suggestion,  training,  and  imitation  is 
made  possible  by  the  association  maintained  by  the  social  group.  It 
is  a  universal  fact  that  the  social  characteristics  of  individuals  of  the 
same  associating  group  are  gradually  unified  by  association.  Again, 
it  is  certain  that  a  group  of  freely  associating  and  freely  intergenerat- 
ing  individuals  of  different  races  of  mankind  will  in  time  become  assimi- 
lated in  language,  manners,  and  customs,  and  finally  in  race,  however 
different  they  may  have  been  when  first  brought  together.  The 
blending  of  two  strongly  marked  species  is  usually  prevented  either 
by  instinctive  aversion,  by  unfruitful  crossing,  or  by  the  sterility  of 
the  hybrid  offspring,  as  in  the  case  of  the  mule;  while  the  blending  of 
two  civilizations  is  liable  to  be  prevented  by  the  superior  power  of  one 
completely  overshadowing  the  influence  of  the  other.  Moreover  as 
long  as  racial  barriers  are  not  broken  down,  distinctions  of  social 
types  are  not  often  wholly  obliterated.  This  is  naturally  the  case  as 
long  as  the  training  of  the  young,  and  so  the  transmission  of  tradition, 
remains  chiefly  with  the  parents. 

Segregate  association,  that  is,  the  association  of  like  with  like,  is 
the  fundamental  factor  in  the  production  of  habitudinal  segregations ; 

*  That  is,  the  association  with  each  other  of  individuals  with  hke  acquired  char- 
acters. 


THE  INTERACTION  OF   RACIAL    AND  SOCIAL   EVOLUTION.  49 

and,  as  will  be  more  fully  explained  in  another  chapter,  it  is  brought 
about  by  the  cooperation  of  habitudinal  demarcation  through  parti- 
tion, and  habitudinal  intensification  through  election.  The  methods  of 
this  election  are  first  through  the  different  forms  of  approval  and  disap- 
proval used  in  training  the  young,  and  second  through  the  promotion 
and  wide  influence  given  to  individuals  attaining  the  highest  recog- 
nition of  public  opinion  and  the  suppression  of  individuals  falling 
below  the  lower  limits  set  by  the  laws  and  customs  of  the  community. 

Divergent  forms  of  civilization  can  neither  be  established  nor  main- 
tained without  the  continuous  operation  of  segregate  association. 

For  designating  the  effects  of  segregate  association  I  often  use  the 
term  "habitudinal  segregation"  rather  than  "social  segregation," 
because  in  creatures  entirely  guided  by  instinct  there  may  be  elab- 
orate forms  of  social  organization,  and  therefore  forms  of  social  segre- 
gation, that  rest  mainly,  if  not  entirely,  on  racial  characters  produced 
by  racial  segregation;  while  under  "habitudinal  segregation"  I  wish 
to  consider  the  evolution  of  acquired  characters  under  the  operation  of 
segregate  association.  If  ants  and  bees  learn  by  training  and  imita- 
tion incorporated  in  traditions,  then  the  growth  of  their  social  organ- 
izations should  be  treated  under  this  department  of  segregation ;  but, 
if  not,  then  their  evolution,  both  physical  and  social,  comes  under  the 
department  of  racial  segregation. 

4.   The  Interaction  of  Racial  and  Social  Evolution  must  be  considered. 

The  interaction  of  racial  and  social  (or  habitudinal)  evolution  and 
the  exposition  of  the  laws  regulating  the  same,  by  which  man  is  to 
gain  control  of  his  own  evolution,  is  the  broad  sphere  in  which  the 
biology  and  sociology  of  the  future  will  expand.  Ward,  Giddings, 
Baldwin,  and  other  Americans  are  exploring  this  field,  and  in  Europe 
the  trend  is  in  the  same  direction,  if  I  judge  rightly.  The  nomen- 
clature which  I  propose  and  illustrate  in  the  following  pages  will,  I 
think,  aid  in  discussing  the  problems  of  biology  and  sociology  that  are 
now  coming  to  the  front.  I  should  not  have  had  the  patience  and 
courage  to  attempt  to  present  a  scheme  for  so  wide  a  field  if  I  had  not 
seen  the  pressing  need  for  such  a  method  from  the  side  of  biology.  I 
also  believe  it  will  be  a  great  advantage  for  sociology  if  a  harmonious 
and  correlated  nomenclature  can  be  brought  into  use  in  both  biology 
and  sociology.  Some  sociologists,  recalling  the  nomenclature  and 
exposition  introduced  by  Herbert  Spencer  on  the  basis  of  an  assumed 
correspondence  between  the  biological  and  the  social  organism,  will 
instinctively  shun  the  use  of  a  terminology  that  suggests  a  correspon- 
dence and  interdependence  between  the  two  spheres  of  evolution. 
There  will,  however,  be  others,  who  have  come  into  sufficiently  close 


50  THE   FOUR   SEGREGATIVE    PRINCIPLES. 

contact  with  the  problems  of  evolution,  in  both  realms,  to  realize  that 
great  illumination  for  each  will  be  found  in  the  study  of  the  interac- 
tion between  the  two  realms.  Those  who  are  doubtful  concerning 
the  interaction  of  the  two  spheres  will  gain  light  from  Baldwin's 
Social  and  Ethical  Interpretations  and  his  Development  and  Evolu- 
tion, and  from  the  discussions  on  organic  selection  given  by  Osborn, 
Baldwin,  and  others  in  Science  and  The  American  Naturalist  during 
1896-98.  A  clear  exposition  of  "organic  selection"  is  also  given  in 
Conn's  "Methods  of  Evolution,"  a  work  presenting  with  remarkable 
fairness  the  results  reached  by  different  schools  of  biologists,  and  the 
same  subject  is  discussed  by  Lloyd  Morgan  in  his  volume  entitled 
"Habit  and  Instinct,"  especially  in  the  last  four  chapters. 

5.  Determinate  Evolution  of  Evolutionary  Terminology. 

With  gradually  advancing  clearness,  the  relations  of  the  two 
spheres  of  evolution  to  each  other  have  been  recognized,  while  at  the 
same  time  the  necessity  for  a  distinct  nomenclature  for  the  processes 
shaping  the  evolution  in  each  sphere  has  been  increasingly  realized 
and  in  some  degree  provided  for.  On  the  one  hand  variation,  hered- 
ity, and  adaptation  have  been  restricted  in  their  application  to  pro- 
cesses and  powers  by  which  racial  characters  are  produced,  and  on 
the  other  hand  the  correlative  terms  "  innovation,"*  "tradition,"!  ^nd 
"  accommodation  "|  have  been  introduced  to  designate  analogous  pro- 
cesses by  which  acquired  characters  are  produced.  There  remains, 
however,  much  confusion  due  to  attempts  to  extend  the  scope  of  the 
term  "  selection  "  so  as  to  include  the  processes  by  which  social  habits 
and  customs  are  established;  and  sometimes  even  to  designate  pro- 
cesses that  properly  come  under  the  term  "isolation."  I  believe  the 
only  remedy  will  be  found  in  the  introduction  of  two  terms  that  shall 
take  the  place  in  the  theory  of  the  evolution  of  habitudes  that  isola- 
tion and  selection  fill  in  the  theory  of  the  evolution  of  aptitudes.  The 
advance  toward  this  end  is,  I  believe,  an  evolution  that  can  not  be 
stayed.  What  terms  will  eventually  prevail  is  a  matter  of  less  cer- 
tainty and  of  less  importance. 

The  scheme  presented  in  this  chapter  is  offered  by  way  of  sugges- 
tion and  with  the  hope  that  it  may  lead  to  suggestions  from  others, 
and  thus  help  in  the  attainment  of  a  completer  theory  and  better 
nomenclature  than  any  now  in  use.  As  has  been  said  by  Prof.  E.  O. 
Whitman,  "Cross-fertilization  works  rejuvenation  in  theories  as  in 
organisms." 


*  See  Tarde's  Social  Laws,  pp.  40,  52. 

t  See  Baldwin's  Development  and  Evolution,  p.  152. 

X  Ibid.,  p.  151. 


THE  IMPORTANCE  OF  ISOLATION.  51 

II.     Segregation  the  Combined  Result  from  Four  Principles. 
1.  Racial  Segregation  Controlled  by  Two  Principles,  and  Habitudinal 
Segregation  by  Two. 

Racial  or  aptitudinal  segregation  rests  on  heredity  and  variation, 
and  is  controlled  by  segregate  intergeneration  of  individuals  accord- 
ing to  their  inherited  characters;  while  social  or  habitudinal  segre- 
gation rests  on  tradition  and  innovation  and  is  controlled  by  segre- 
gate association  of  individuals  according  to  their  acquired  charac- 
ters. The  control  of  variation  and  heredity  rests  directly  upon  the 
limitations  of  segregate  intergeneration  produced  by  the  two  princi- 
ples, racial  demarcation  through  isolation  and  racial  intensification 
through  survival  (in  its  two  forms,  selection  and  indiscriminate  elimi- 
nation). The  control  of  tradition  and  innovation  rests  upon  the 
limitations  of  segregate  association  produced  by  the  two  principles, 
habitudinal  demarcation  through  partition  and  habitudinal  intensi- 
fication through  success  (in  its  two  forms,  election  and  indiscriminate 
failure).  We  have,  therefore,  four  main  principles  cooperating  in  the 
production  of  segregate  types,  namely,  partition,  success,  isolation, 
and  survival.  In  order  to  understand  the  evolution  of  sexually 
reproducing  organisms  it  is  necessary  to  gain  clear  conceptions  of 
these  four  principles  and  of  their  relations  to  each  other  in  producing 
the  ramified  and  intensified  segregation  of  types.  Each  of  these  prin- 
ciples when  called  into  action  has  more  or  less  influence  on  the  control 
of  segregate  generation,  and,  therefore,  influence  on  the  types  of  the 
organism. 

2.   The  Importance  of  Isolation. 

The  importance  of  isolation  as  a  coordinate  factor  with  selection  in  the 
evolution  of  species  is  now  gaining  wide  recognition.  Romanes'  expo- 
sition of  the  subject,  given  in  Darwin  and  After  Darwin,  Part  III,  is 
so  convincing  that  an  increasing  number  of  English  and  American 
biologists  are  disposed  to  grant  the  general  soundness  of  the  claim 
that  the  prevention  of  free  crossing  is  a  necessary  principle  in  the 
divergent  evolution  of  races  and  species ;  but  some  of  the  same  writers 
are  not  satisfied  with  the  nomenclature  which  Romanes  has  adopted 
in  setting  forth  the  doctrine.  In  the  first  place,  he  fails  to  discriminate 
clearly  between  selection  and  isolation.  This  has,  I  think,  arisen 
from  following  the  custom  of  describing  any  influence  that  tends  to 
transform  species  as  a  form  of  selection.  Following  this  method, 
Karl  Pearson  defines  sexual  selection  as  including  ' '  all  differential 
mating  due  to  taste,  habit,  or  circumstance  which  prevents  a  form  of 
life  from  freely  intercrossing."*     Following  the  same  method  Ro- 


*  See  Grammar  of  Science,  p.  417 


52  THIS  FOUR  SEGREGATIVE   PRINCIPLES. 

manes  says  of  infertility  between  varieties  of  the  same  species :  ' '  For 
the  sake  of  convenience,  and  in  order  to  preserve  analogies  with 
already  existing  terms,  I  will  call  this  principle  physiological  selection 
or  segregation  of  the  fit."*  Since  the  publication  of  his  essay  on 
Physiological  Selection  in  1886,  and  of  my  papers  on  Divergent  Evo- 
lution and  Intensive  Segregation  in  1887  and  1889,  isolation  has  by 
general  consent  come  to  mean  the  prevention  of  free-crossing  between 
groups  existing  at  the  same  time.  In  accordance  with  this  usage,  in 
Darwin  and  After  Darwin,  Romanes  often  substitutes  physiological 
isolation  for  physiological  selection,  which  is  a  great  gain.  When, 
however,  he  gives  a  precise  definition  of  isolation,  he  extends  its 
meaning  so  as  to  include  the  prevention  of  crossing  between  those 
members  of  the  group  who  succeed  in  living  and  propagating  and 
those  who  die  without  -  propagating.  This  definition  of  isolation 
makes  it  include  natural  selection  as  one  of  its  many  forms.  (See 
Darwin  and  After  Darwin,  Part  III,  pp.  9,  10.)  I  recognize  most 
fully  the  importance  of  keeping  in  mind  the  fact  that  natural  selec- 
tion would  have  no  power  to  transform  species  if  it  did  not  prevent 
the  crossing  of  the  fit  with  the  unfit;  but  I  think  the  relation  of  the 
different  factors  can  be  best  presented,  first,  by  restricting  the  term 
"  selection  "  to  the  influences  that  determine  the  survival  (that  is,  the 
continued  propagation)  of  the  fit  innate  variations  of  any  given 
group,  and  the  elimination  (that  is,  the  disappearance)  of  the  unfit, 
thus  preventing  the  crossing  of  the  fit  with  the  unfit;  second,  by 
restricting  the  term  isolation  to  the  prevention  of  free  crossing  be- 
tween groups  existing  at  the  same  time;  and  third,  by  showing  how 
these  two  principles  cooperate  in  producing  racial  segregation  of  the 
fit  which  is  the  essence  of  racial  evolution.  The  conception  of  racial 
evolution  which  I  thus  expound  is  much  the  same  as  that  presented 
by  Romanes;  but,  if  I  mistake  not,  the  meanings  which  I  attach  to 
the  different  terms  are  in  better  accord  with  general  usage.  I  also 
attempt  a  wider  problem,  in  that  I  now  add  to  my  exposition  of 
racial  segregations  and  amalgamations  a  similar  analysis  of  habitudi- 
nal  segregations  and  amalgamations,  with  the  special  purpose  of 
bringing  clearly  into  view  the  action  and  reaction  between  the  two 
spheres  of  evolution.  I  think  that  even  the  most  conservative  biolo- 
gists are  coming  to  recognize  with  Mr.  Headley  that  the  racial  evolu- 
tion of  the  higher  animals,  and  especially  of  man,  is  guided  by  their 
social  evolution  (or  by  their  progress,  as  he  would  put  it),  while  many 
already  agree  with  him  in  his  statement  that  "If  natural  selection 
works  without  isolation,  only  monotypic  evolution  can  result."! 

*  Journal  Linnean  Society,  Zoology,  Vol.  XIX,  p.  354. 
t  See  Problems  of  Evolution,  pp.  128,  175. 


DEFINITIONS  OF  THE   FOUR  SEGRKGATIVE   PRINCIPI^ES.  53 

3.  Definitions  of  the  Four  Segregative  Principles. 

First.  Partition  is  the  setting  of  individuals  in  groups,  the  members 
of  each  group  associating  with  each  other  and  securing  what  Pro- 
fessor Giddings  calls  "socialization,"  and  what  Professor  Baldwin 
calls  "social  generalization,"  through  learning  from  each  other. 

Second.  Success  (of  which  election  is  the  discriminate,  and,  therefore, 
the  more  important  form) .  Election  is  the  superior  influence  of  such 
individuals  as  have  best  attained  the  ideals,  habitudes,  and  acquired 
characters  fitting  them  for  individual  success  and  leadership;  and 
the  inferior  success  and  influence  of  those  that  are  deficient  in  the 
same  ideals,  habitudes,  and  acquired  characters.  The  term  ' '  imitative 
selection"  has  been  defined  by  Professor  Baldwin  as  produced  by 
"imitative  propagation  from  mind  to  mind  with  social  heredity"; 
and  as  resulting  in  "survival  of  ideas  in  society."*  Imitative  selec- 
tion seems,  therefore,  to  cover,  at  least  in  part,  what  I  call  election. 
I  have  not,  however,  been  able  to  use  it  in  the  analysis  given  in  this 
chapter;  for  in  my  tables  selection  is  applied  only  to  factors  deter- 
mining the  survival  of  innate  variations,  and,  therefore,  influencing 
racial  heredity.  The  indiscriminate  form  of  success  I  usually  call 
indiscriminate  failure ;  for  it  is  most  effective  in  producing  divergent 
types  when  indiscriminate  slaughter,  or  absorption  by  a  more  power- 
ful race,  leaves  only  small  and  isolated  fragments  of  the  original  type 
of  civilization. 

Tarde  emphasizes  the  importance  of  "the  suggestive  and  con- 
tagious influence  of  certain  select  individuals  upon  the  group  as  a 
whole."! 

Third.  Isolation  is  the  setting  of  individuals  in  groups,  the 
members  of  each  group  intergenerating,  and  so  securing  racial 
generalization  (or  fundamental  unity  of  inheritance)  within  each 
group,  while  between  the  groups  there  is  prevention  of  free  crossing. 

Fourth.  Survival  (of  which  selection  is  the  discriminate,  and, 
therefore,  the  more  important  form).  Selection  is  the  survival  (that 
is,  the  continuance  from  generation  to  generation)  of  those  individ- 
uals whose  innate  characters  give  them  the  advantage  over  others  in 
coming  to  maturity  and  reproducing.  It  avails  nothing  in  selection 
for  individuals  to  complete  their  normal  term  of  life,  unless  they 
leave  offspring  in  due  proportion;  and  numerous  offspring  avails 

*  See  Appendix  B,  Social  and  Ethical  Interpretations,  1897;  also  Science,  No- 
vember 19,  1897,  p.  770;  also  Development  and  Evolution,  1902,  p.  166. 

t  See"  Social  Laws,"  p.  46  of  the  translation  published  by  The  MacMillan  Co., 
New  York. 


54  THE    FOUR   SEGREGATIVE    PRINCIPLES. 

nothing  in  determining  selection  unless  they  have  power  to  live  and 
reproduce.  The  indiscriminate  form  of  survival  I  call  "indiscrimi- 
nate elimination."  It  is  often  the  chief  principle  by  which  diver- 
gence is  initiated  in  two  or  more  isolated  masses  of  a  species.  If 
indiscriminate  destruction  reduces  each  group  to  but  one  or  two  indi- 
viduals capable  of  propagating  the  race,  divergence  immediately 
arises  in  regard  to  one  or  more  points  of  character. 

Partition,  acting  on  acquired  characters,  produces  habitudinal  de- 
marcation with  initial  habitudinal  segregation. 

Election,  acting  on  acquired  characters,  produces  intensified  habi- 
tudinal segregation. 

Isolation,  acting  on  inherited  characters,  produces  racial  demarca- 
tion with  initial  racial  segregation. 

Selection,  acting  on  inherited  characters,  produces  intensified  racial 
segregation. 

Partition  and  election  acting  together  produce  cumulative  habitu- 
dinal segregation. 

Isolation  and  selection  acting  together  produce  cumulative  racial 
segregation. 

Partition  and  isolation  acting  together  produce  typal  demarcation 
with  initial  segregation,  both  habitudinal  and  racial. 

Election  and  selection  acting  together  produce  intensified  segrega- 
tion, both  habitudinal  and  racial. 

The  four  principles  acting  together  produce  allogamic  evolution, 
both  habitudinal  and  racial,  through  the  segregation  of  types. 

4.  Objections  that  may  be  Raised  to  the  Terms  Used. 

It  may  be  thought  that  such  terms  as  "partition"  and  "election" 
are  not  needed  in  the  exposition  of  the  process  of  evolution ;  that  the 
whole  process  may  be  considered  as  due  to  selection,  and,  if  influences 
not  recognized  by  Darwin  are  discovered,  they  should  be  designated  as 
forms  of  selection.  My  suggestion  is  that  a  definite  attempt  to  con- 
struct a  nomenclature,  enabling  one  to  set  forth  the  evolution  of  ac- 
quired characters  and  the  influence  of  the  same  on  the  evolution  of 
inherited  characters,  will  show  the  investigator  that  great  gain  in 
brevity  and  clearness  may  be  secured  by  the  use  of  separate  words 
to  designate  the  principles  in  habitudinal  segregation  that  corre- 
spond to  isolation  and  selection  in  racial  segregation.  But,  even  if  the 
need  of  such  terms  is  recognized,  objection  may  be  raised  against  the 
use  of  the  term  "election,"  on  the  ground  that  it  properly  signifies 
the  elevation  of  an  individual  to  a  position  of  influence  by  his  winning 
the  conscious  choice  of  rational  beings,  while  in  the  nomenclature 


INTERACTION   OF   THE)    FOUR    PRINCIPLES   OF   SEGRKGATION.      55 

here  proposed  it  is  made  to  cover  superior  influence  over  the  acquired 
characters  of  associates,  whether  the  community  consists  of  rational 
beings  or  not.  A  similar  objection  has  often  been  urged  against  the 
use  of  "selection"  in  the  Darwinian  sense;  but,  on  the  whole,  no 
better  word  has  been  found  to  designate  the  gaining  of  a  full  share  in 
the  propagation  of  the  next  generation,  and  so  a  full  share  of  influence 
on  the  inherited  characters  of  the  community,  whether  it  be  by  win- 
ning the  interest  of  the  rational  part  of  the  environment  or  by  secur- 
ing adaptation  to  other  conditions  in  the  environment.  Each  new 
term  is  an  innovation,  and  like  all  innovations  must  prove  its  useful- 
ness before  it  can  prevail  or  be  elected. 

III.     Inter.\ction  of  the  Four  Principles  of  Segregation. 

1.  Increased  Effects  Produced  by  the  Repeated  Action  of  One  Principle  or  tkp 
Combined  Action  of  More  than  One. 

Mr.  Headley  says  that,  in  my  terms  "intensive  segregation"  and 
"cumulative  segregation"  the  words  "intensive"  and  "cumulative" 
are  "misapplied."  (See  Problems  of  Evolution,  p.  178.)  I  think  his 
criticism  is  chiefly  due  to  his  having  failed  to  note  the  definitions  I 
have  given  to  the  terms  and  the  way  in  which  I  have  applied  them. 
Intensive  segregation  I  have  described  as  due  to  natural  selection  and 
the  other  principles,  producing  transformation  when  cooperating  with 
isolation.*  Cumulative  segregation  is  due  to  a  succession  of  isolations 
coming  at  long  intervals,  in  which  each  isolation  opens  the  way  for 
the  formation  of  some  new  habit  shaping  the  method  of  dealing  with 
the  environment,  and,  therefore,  leads  to  the  formation  of  a  divergent 
species.  For  example,  if  a  variable  species  of  snails,  having  but  little 
opportunity  for  transportation  beyond  the  limits  of  the  valley  it  in- 
habits, and  no  power  for  migration  beyond  the  same,  finds  its  habitat  in 
the  groves  at  one  end  of  the  chief  mountain  range  of  the  island  of  Oahu, 
it  may  become  well  adapted  to  the  conditions  before  a  branch  colony 
is  planted  in  the  next  valley.  Though  the  vegetation  is  the  same  in 
the  two  valleys,  the  new  colony  may  be  started  by  a  single  individual, 
whose  habits  lead  it  to  prefer,  for  food  and  shade,  some  species  of 
plant  that  is  but  little  used  by  the  mother  colony,  and  thus  divergent 
forms  of  endonomic  selection  shape  the  two  colonies  into  two  species. 
After  many  years  the  transportation  of  an  individual  from  the  second 
colony  may  result  in  the  planting  of  a  third  colony  with  still  further 
divergent  habits;  and  so  on  till  the  valleys  at  the  opposite  end  of  the 
mountain  range  have  become  the  habitat  of  species  very  closely  re- 

*  See  Appendix  I,  Section  VII,  3;  also  Appendix  II,  Section  I,  8. 


56  the;  four  segregative  principles. 

lated  to  each  other,  but  quite  distinct  from  the  mother  species  from 
which  they  have  been  separated  by  many  successive  isolations. 

Mr.  Headley  recognizes  that  there  may  be  change  in  the  species 
without  change  in  the  environment  in  what  he  says  concerning  ' '  alter- 
native methods  of  adjustment  to  the  same  environment"  (p.  149).  He 
illustrates  this  in  the  following  way :  ' '  For  many  butterflies,  birds  [that 
prey  upon  them]  are  an  important  part  of  the  environment.  They 
may  adjust  themselves  to  it  (i)  by  developing  great  powers  of  flight, 
or  (2)  an  offensive  taste,  or  (3)  they  may  'mimic'  another  nauseous 
species,  or  (4)  come  to  resemble  some  such  thing  as  a  dead  leaf  and  so 
be  protectively  colored"  (pp.  147,  148).  This  power  which  is  here 
recognized  by  Mr.  Headley  as  belonging  to  many  species  fully  justifies 
his  statement  that ' '  Often  there  is  a  variety  of  possible  adaptations  to 
one  and  the  same  environment"  (p.  146).  How,  then,  can  he  defend 
the  following  sweeping  generalization  given  by  him  in  many  passages, 
on  widely  separated  pages?  I  will  quote  only  two  or  three.  "If  the 
environment  remains  unaltered,  evolution  ceases.  *  *  *  Further 
evolution  can  take  place  only  if  an  environment  that  is  in  some  way 
different  offers  itself"  (p.  103).  "Each  successive  step  of  evolution  is 
due  to  some  change  in  the  environment"  (p.  11 1).  "Nothing  but 
change  of  environment  can  lead  to  further  evolution"  (p.  153). 

Notwithstanding  this  inconsistency  in  his  interpretations,  he  gives 
us  many  fresh  and  interesting  facts. 

2.  Importance  of  Each  of  the  Principles. 

It  is  not  easy  to  determine  whether  each  and  all  of  these  four  prin- 
ciples began  to  control  evolution  from  the  very  dawn  of  life ;  but  when 
once  fully  established  we  find  them  cooperating  in  such  a  way  that  it 
seems  impossible  to  overestimate  the  importance  of  each  in  its  own 
sphere  of  action.  It  is  now  generally  recognized  that  monotypic  evo- 
lution, that  is,  the  transformation  of  any  single  type  into  a  succession 
of  forms  through  which  it  gradually  passes  without  branching,  is 
largely  due  to  selection;  but,  in  a  world  where  two  or  more  species 
exist,  even  in  the  case  of  monotypic  evolution,  the  whole  process  is 
also  dependent  on  isolation ;  for  if  the  single  type  under  consideration 
freely  crosses  with  other  types,  it  loses  its  separate  identity.  In  a 
world  of  diverse  types  the  monotypic  evolution  of  any  one  type  is, 
therefore,  necessarily  a  process  of  intensive  segregation,  in  which  iso- 
lation and  the  principles  producing  transformation  (of  which  selection 
and  election  are  the  chief)  cooperate.  Since  sexual  reproduction 
began  heredity  has  been  controlled  by  the  segregate  generation  of 
individuals  according  to  their  innate  aptitudes  for  adaptive  response ; 
and  isolation  and  selection  have  cooperated  in  producing  segregate 


IMPORTANCE    OF   KACH    OP   THE   PRINCIPLES.  57 

generation,  and  so  in  intensifying  the  aptitudes.  What,  then,  shall  we 
say  of  the  segregate  association  of  individuals  according  to  their  habi- 
tudes, acquired  by  experimental  initiation,  individual  repetition,  social 
imitation,  and  other  methods  of  accommodation  opening  to  the  differ- 
ent groups  divergent  methods  of  dealing  with  the  environment;  and 
what  of  the  partition  and  election  which  cooperate  in  producing  the 
segregate  association,  and  so  in  intensifying  the  acquired  adjustments? 
Did  the  individuals  of  the  primitive  form  or  forms  of  life  possess 
powers  that  were  in  any  way  or  in  the  least  degree  discriminative? 
Had  they  any  power  to  select  that  which  is  needed  and  to  reject  that 
which  is  useless  or  detrimental  ?  And  when  the  environment  became 
somewhat  complex,  had  the  same  species  power  to  divide,  one  section 
establishing  close  relations  with  one  part  of  the  environment  and 
another  section  with  another  part  of  the  environment?  If  the  correct 
answers  to  these  questions  are  in  the  affirmative,  then  from  early  times 
habitudinal  segregation,  in  its  two  forms,  partition  and  election,  have 
had  an  important  influence  on  racial  segregation,  and,  therefore,  on  the 
evolution  of  innate  aptitudes. 

In  the  production  of  segregated  racial  types  isolation  seems  to  be 
the  most  essential  of  the  four  principles,  for  there  can  be  no  racial 
segregation  where  there  is  no  isolation,  while  there  may  be  cases  of 
segregation  and  divergence  (at  least  for  a  number  of  generations)  that 
are  not  at  all  dependent  on  new  methods  of  action  of  any  one  or  more 
of  the  other  three  principles.  Such  a  case  occurs  when  some  peculiar 
variation  or  mutation,  being  transported  to  a  position  where  there  is 
no  opportunity  of  crossing  with  other  varieties,  propagates  its  own 
peculiarity  for  many  generations,  though  exposed  to  the  same  external 
conditions  as  the  body  of  the  species  from  which  it  has  been  separated. 
If,  however,  the  isolation  is  continued  through  a  long  series  of  genera- 
tions, new  forms  of  selection  inevitably  arise,  and  in  time  new  forms 
of  acquired  character  resulting  from  new  forms  of  activity  and  new 
forms  of  direct  stimulus  from  the  environment;  and  in  this  way 
the  initial  segregation  produced  by  the  isolation  is  intensified  by 
diverse  forms  of  selection  and  by  modifications  resulting  from  estab- 
lished habits.  Moreover,  the  acquired  characters  may  become  the 
active  agency  leading  to  new  groupings  of  individuals,  and  in  many 
cases  these  new  groupings  introduce,  or  are  accompanied  by,  group- 
ings according  to  natural  aptitudes  and  other  innate  endowments. 
In  other  words,  using  the  terms  just  indicated,  we  start  with  isolation, 
which  opens  the  way  for  divergent  forms  of  selection,  and  the  new 
forms  of  selection  lead  to  new  forms  of  partition,  and  these  lead  to 
new  forms  of  isolation,  thus  establishing  a  circle  of  influences.     Again, 


58  THE   I^OUR   SEGREGATIVE    PRINCIPLES. 

new  forms  of  partition  open  the  way  for  diverse  forms  of  election, 
which  result  in  the  success  of  divergent  habitudes  in  the  sepa- 
rated groups;  and  these  divergent  habitudes  may  bring  the  individ- 
uals to  whom  they  belong  into  positions  producing  isolation,  and  into 
divergent  methods  of  dealing  with  the  environment,  and  so  subject 
them  to  divergent  forms  of  selection  producing  divergent  racial  evo- 
lution. 

We  therefore  observe  that,  in  the  evolution  of  the  higher  types  of 
animals,  each  of  these  four  principles  must  have  a  most  important 
part;  for,  in  producing  divergent  racial  types,  isolation  is  absolutely 
essential,  and  partition  is  the  forerunner  preparing  the  way  for  isola- 
tion. Again,  selection  usually  operates  in  each  generation,  either  in 
giving  emphasis  and  stability  to  types  already  attained,  of  in  mold- 
ing the  separate  groups  created  by  partition  and  isolation,  according 
to  new  necessities,  which  are,  in  most  cases,  introduced  by  the  new 
experiments,  new  attainments,  and  new  habitudes  that  have  been 
established  by  the  different  forms  of  election.  My  interpretation  of 
these  factors  does  not  tend  toward  the  minimizing  of  the  importance 
of  selection;  but  it  shows  that  isolation,  partition,  and  election  are  of 
equal  importance  in  their  own  spheres.  It  shows  that  the  transfor- 
mation of  forms  that  do  not  freely  intergenerate  is  always  more  or  less 
divergent,  and  that  the  racial  divergence  of  any  two  forms  is  absolutely 
dependent  on  isolation,  i.  e  ,  the  prevention  of  free  crossing.  It  fur- 
ther emphasizes  the  fact  that  selection,  both  in  its  reflexive  and  its 
environal  forms,  is  in  a  large  degree  controlled  by  the  varying  habi- 
tudes and  aptitudes  of  different  sections  of  a  species,  so  that  the  iso- 
lated portions  of  a  variable  species  would  in  time  develop  different 
forms  of  selection,  even  if  they  could  be  exposed  to  absolutely  similar 
environments.  These  points  are  all  presented  in  full  in  the  paper 
reproduced  in  Appendix  II,  but  the  new  nomenclature  here  introduced 
facilitates  our  apprehension  of  the  facts. 

3.   The  Two  Methods  of  Generalization. 

Racial  generalization  is  produced  by  heredity  with  free  crossing 
within  the  bounds  of  each  racial  group.  Hahitudinal  generalization 
is  produced  by  tradition  with  free  association  within  the  bounds  of  the 
social  group.  The  influence  of  heredity  is  so  fully  recognized  that  we 
need  not  stop  to  illustrate  the  fact  that  two  or  more  somewhat  diver- 
gent types,  when  freely  intergenerating  for  many  generations,  will  be 
reduced  to  a  single  racial  (or  aptitudinal)  type  which  is  perpetuated 
with  considerable  constancy  from  generation  to  generation.  It  is  also 
manifest  that  tradition,  which  transmits  the  habits  of  each  generation 
to  the  next,  through  the  training  and  suggestion  given  by  parents  to 


CHANGE   OF  TRADITION  IN  THE  CASE  OF  CHIMNEY  SWIFT.         59 

their  offspring  and  by  the  experienced  leaders  to  the  multitude,  and 
responded  to  by  the  instinct  for  imitation  possessed  by  the  young  and 
inexperienced,  will  establish  and  perpetuate  a  more  or  less  constant 
social,  or  habitudinal,  type.  And  it  should  be  especially  noted  that 
the  habits  thus  transmitted  from  generation  to  generation  determine 
the  relations  of  the  group  to  the  environment,  and,  therefore,  the  form 
of  selection  that  continues  with  cumulative  results  in  successive  gene- 
rations. The  influence  of  habitudinal  generalization  is  illustrated  by 
the  following  case: 

4.  Change  of  Tradition  in  the  Case  0}  the  Chimney  Swift. 

The  chimney  swift  of  eastern  North  America,  often  called  the  chim- 
ney swallow,  has  made  an  important  change  in  its  habits  since  the 
settling  in  this  region  of  Europeans  who  build  houses  with  chimneys. 
We  know  that  before  the  coming  of  the  European  the  traditions  of  this 
bird  determined  that  hollow  trees  should  be  occupied  as  the  appro- 
priate places  for  their  nest-building.  How  the  present  tradition,  giv- 
ing the  preference  to  chimneys,  was  started,  we  are  not  informed ;  but 
we  may  believe  that  a  pair  of  birds  of  an  investigating  spirit,  finding 
that  the  hollow  trees  in  which  they  and  their  ancestors  had  been  in  the 
habit  of  building  had  been  cut  down,  ventured  to  make  the  new  experi- 
ment. Being  rewarded  with  success,  election  is  on  their  side,  and 
their  descendants  survive  to  perpetuate  the  habit.  Other  birds  of 
the  same  species  see  their  success  and  follow  their  example;  and  as 
chimneys  are  multiplied,  while  hollow  trees  are  diminished  in  number, 
the  followers  of  the  new  habit  in  time  outnumber  the  adherents  to 
the  old  tradition,  and  from  that  time  on  the  old  conservative  habits 
crumble  rapidly  away.  The  vast  majority  of  the  species  have  now 
abandoned  the  old  tradition,  and  the  newer  tradition  now  prevails 
everywhere,  except  in  the  Dismal  Swamp  (a  region  about  30  miles  in 
length  and  10  miles  in  width,  in  the  States  of  Virginia  and  North  Caro- 
ina),  where  their  unconscious  helper  has  failed  to  erect  his  chimneys. 

5.  The  Two  Methods  of  Adjustment. 

Aptitudes  are  inherited  forms  of  adaptation  resulting  from  tentative 
variations  accumulated  by  the  survival  of  the  fittest.  Habitudes  are 
traditional  accommodations  (that  is,  traditional  forms  of  adjustment), 
resulting  from  tentative  innovations  accumulated  by  repetition  and 
imitation  of  successful  experiments. 

Adaptation  in  plants  and  in  the  lower  types  of  animals  is  gained 
chiefly  by  variation  in  the  degrees  of  innate  qualities  and  in  the  inten- 
sity of  innate  activities,  molded  in  successive  generations  by  the  sur- 
vival of  individuals  having  the  fittest  endowmentsjin  each  isolated 


6o  THE   FOUR  SEGRKGATIVE   PRINCIPLES. 

group.  This  molding  of  variation  and  heredity  by  isolation  and  selec- 
tion results  in  racial  segregations.  But  even  plants  are  endowed  with 
powers  that  enable  each  individual  to  do  something  toward  directly 
adjusting  itself  to  the  environment  in  which  it  is  placed,  for  they  will 
stretch  their  branches  and  turn  their  leaves  toward  the  light,  and  their 
roots  will  bend  toward  moisture  and  away  from  hard  or  irritating 
substances  obstructing  their  course.  This  power  of  the  individual 
for  experimental  action  with  ability  to  persist  in  the  action  that  secures 
the  best  results  is  called  accommodation;  and  the  molding  of  accom- 
modation and  tradition  into  habitudes  produces  habitudinal  segrega- 
tions with  their  adjustments.  We  find  that  accommodation  fills  a 
sphere  of  increasing  importance  in  the  evolution  of  animals  according 
to  the  degree  of  their  mental  endowments.  In  studying  the  evolution 
of  the  higher  animals  it  is  especially  necessary  to  consider  the  adjust- 
ments produced  through  the  molding  of  accommodations  by  election, 
as  well  as  those  produced  by  the  molding  of  variations  by  selection. 
The  importance  of  prolonged  infancy  and  childhood  in  mankind  has 
been  rightly  emphasized  by  John  Fiske;  but  the  significance  of  this 
condition  is  found  in  its  opening  the  way  for  the  building  of  habits 
guided  by  the  experience  of  many  generations.  The  combined  wis- 
dom of  countless  ancestors  thus  is  transmitted  to  the  young  through 
language,  example,  and  training,  formulated  in  maxims,  and  customs, 
in  penalties  and  rewards,  and  instilled  into  minds  specially  endowed 
with  powers  of  imitation  and  with  aptitudes  for  forming  lasting  habits ; 
and  the  process  is  continued  much  longer  than  in  the  case  of  animals 
lower  than  man.  In  the  case  of  beasts  and  birds  the  equipment  for 
the  struggle  of  life  is  received  in  a  larger  degree  through  inherited 
powers  and  instincts,  though  tradition  is  also  of  importance. 

6.  The  Two  Methods  of  Adjustment  as  Applied  to  New  Conditions,  SvddenLy 
or  Gradually  Encountered. 

I  have  already  considered  certain  cases  involving  resources  that  are 
varied  but  familiar  to  the  species  and  easily  explored,  in  which  habi- 
tudes (that  is,  traditional  forms  of  accommodation),  and  aptitudes 
(that  is,  inherited  forms  of  adaptive  variation),  become  the  control- 
ling factors  in  determining  selection.  We  wish  now  to  consider  cases  in 
which  the  new  environment  fails  to  present  the  conditions  and  resources 
to  which  the  organism  has  been  accustomed.  In  the  first  place,  if 
the  species  has  but  slight  accommodative  power,  and  the  new  condi- 
tions are  suddenly  encountered,  habitudes  and  aptitudes  will  be  of 
little  or  no  avail  in  guiding ;  and,  though  some  of  the  variations  may 
be  able  to  battle  with  the  new  conditions  for  a  generation  or  two,  none 
will  be  able  to  survive  and  propagate  permanently. 


TWO   METHODS   OF   MEETING   NEW  CONDITIONS.  6l  * 

In  the  second  place,  if  the  new  conditions  are  slowly  introduced, 
as  is  often  the  case  in  geoloj^ical  chanf^es,  innate  variation,  combined 
with  high  reproductive  powers,  may  enable  them  to  meet  the  changes  as 
well  as  do  those  endowed  with  much  higher  powers  of  accommodation ; 
but  in  cases  of  sudden  change,  high  powers  of  accommodation  will 
often  preserve  the  group  from  extinction  till  time  has  been  given  for 
the  accumulation  of  what  Lloyd  Morgan  has  called  "coincident  varia- 
tions."* When  acconnnodalion  thus  opens  the  way  for  sttccessful 
selection.  Professor  Baldwin  calls  the  process  "organic  selection."  I 
am  disposed  to  raise  the  question  whether  the  term  "coincident  varia- 
tion," suggested  by  Lloyd  Morgan,  docs  not  meet  the  case  more  ex- 
actly; and  when  the  variations  are  accumulated,  may  it  not  be  well 
to  call  the  process  "coincident  selection"?  Let  it,  however,  be  care- 
fully noted  that  a  slow  change  of  conditions,  either  in  the  relations  of 
the  organism  to  the  environment  or  in  the  relations  of  the  individuals 
of  the  organism  to  each  other,  may  result  in  the  gradual  transforma- 
tion of  slightly  varying  habitudes  and  aptitudes  through  election  and 
selection,  even  when  the  range  of  individual  accommodation  is  very 
small,  and  when  the  degree  of  variation  in  inherited  qualities  is  not 
large,  in  any  one  generation. 

7.  In  the  case  0}  Civilized  Man,  especially  when  exposed  to  sudden  cliange, 
Accommodation  overshadows  and  controls  all  other  influences:  (i)  by 
Organic  Selection,  that  is,  by  giving  time  for  the  action  of  Natural  Selution, 
and  (2)  by  the  success  of  Accommodation  and  Tradition,  removing  the  need 
of  special  variation  in  order  to  survive. 

The  great  importance  of  accommodation  is  often  seen  in  birds  and 
mammals,  and  pre-eminently  in  man.  The  power  of  man  to  occupy 
every  land,  of  every  clime,  that  is  not  entirely  devoid  of  vegetation,  or 
continuously  capped  with  ice,  is  due  to  his  powers  of  accommodation. 
By  accommodation  he  overcomes  his  enemies;  by  accommodation  he 
wins  nourishment  in  hitherto  untried  fields;  by  accommodation  he 
protects  himself  against  the  extremes  of  heat  and  cold,  to  which  he 
would  soon  succumb  if  fortified  simply  by  the  inherited  characters  of 
his  body  thus  far  attained,  unaided  by  artificial  clothing  and  shelter. 
But  even  in  the  case  of  man,  who  is  able  by  his  arts  to  adjust  himself 
to  great  extremes  of  climate,  there  have  arisen  diflerent  races,  with 
special  adaptations  to  diflerent  climates  in  their  inherited  characters. 
If  the  average  child  of  tropical  Africa  and  the  average  child  of  Green- 
land should  exchange  homes  and  training,  both  would  be  heavily 

♦  See  "Habit  and  Instinct"  (London,  1896),  pp.  3i2ff;  also  "Animal  Rcliavior" 
(i9cx3),  pp.  39,  115;  also  Baldwin's  "Development  and  Evolution,"  Appendix  A. 


62  THE   FOUR   SEGREGATIVE   PRINCIPLES. 

handicapped  in  the  struggle  for  Hfe,  through  lack  of  innate  adaptation. 
Man  was  probably  fully  adapted  in  constitutional  character  to  warm 
climates  before  the  arts  of  clothing  and  house-building  had  arisen; 
but  we  may  well  believe  that  these  arts  were  found  of  the  utmost 
importance  when  ti  ibes  began  to  invade  the  colder  climates,  or  when 
cold  weather  invaded  their  native  lands;  and  that  it  was  in  conse- 
quence of  these  arts  that  permanent  colonies  in  the  colder  regions 
became  possible.  How  then  shall  we  account  for  the  constitutional 
adaptations  of  the  Eskimo  race — adaptations  extending  even  to  the 
tissues  of  the  body,  so  that  they  are  incased  with  a  layer  of  fat  just 
beneath  the  skin,  rendering  the  same  kind  of  protection  from  the  cold 
that  the  whale  receives  from  his  blubber?*  It  seems  probable  that 
we  have  in  this  case  an  illustration  of  the  way  in  which  accommoda- 
tion prepares  for,  and  leads  up  to,  certain  conditions  producing  selec- 
tion. In  the  remote  ancestors  of  the  Eskimo,  the  habit  of  protecting 
from  the  cold  by  clothing  and  other  arts  undoubtedly  preceded  the 
establishing  of  the  racial  characters  by  which  they  are  now  in  a  meas- 
ure protected;  but  the  devices  of  the  accommodating  faculties  were 
not  sufficient  to  prevent  those  endowed  with  even  slightly  developed 
constitutional  powers  for  withstanding  the  cold  from  enjoying  some 
advantage  in  meeting  the  conditions  of  life,  and  so  being  gradually 
selected.  If  this  is  a  true  interpretation  of  the  case,  it  illustrates 
what  Professor  Baldwin  calls  "organic  selection"  and  Professor  Lloyd 
Morgan  calls  "accumulation  of  coincident  variations."  The  import- 
ance of  this  principle  in  preserving  certain  creatures,  when  subjected 
to  heavy  change  within  the  period  of  any  one  generation,  can  not  be 
questioned.  The  necessity  for  powers  of  accommodation  in  order  to 
meet  successfully  great  changes  is  of  two  kinds:  First,  for  power  to 
provide  against  great  alternations  in  conditions  that  come  to  each  gen- 
eration, such  as  changes  in  temperature  and  changes  in  the  degree  of 
moisture;  and  second,  for  power  to  meet  new  sets  of  conditions,  to 
which  the  race  has,  in  its  previous  experience,  never  been  continuously 
exposed.  For  the  former  of  these  classes  of  changes,  many  species  of 
the  lowest  animals  and  large  numbers  of  plants  are  as  fully  equipped 
as  the  higher  animals,  including  man ;  but  the  nature  of  the  equipment 
is,  in  the  case  of  the  plants,  wholly  physiological,  and,  in  the  case  of 


*  In  "Greenland  Icefields  and  Life  in  the  North  Atlantic,"  by  G.  Frederick 
Wright  and  Warren  Upham,  I  find  the  following  quotation  from  F.  A.  Cook,  eth- 
nologist of  the  first  Peary  North  Greenland  Expedition,  concerning  this  character 
in  the  Eskimo:  "The  muscular  outlines  of  the  body  are  nearly  obHterated  from 
the  fact  that  they  have  immediately  beneath  the  skin  a  layer  of  blubber,  or  areolar 
tissue,  which  protects  them  against  extreme  cold." 


ENDONOMIC  SELECTION   ILLUSTRATED.  63 

the  lower  classes  of  animals,  largely  physiological,  with  some  coordi- 
nated instincts;  while  in  the  case  of  man  the  power  of  adjustment  is 
very  largely  psychological,  and  in  the  case  of  the  other  classes  of  ani- 
mals, above  the  lowest,  physiological  and  psychological  adaptations 
constantly  cooperate.  The  explanation  of  these  inherited  adapta- 
tions of  the  humblest  organism  to  climatic  and  other  conditions  in- 
volving great  fluctuations  is,  I  think,  to  be  found  in  the  fact  that  they 
or  their  ancestors  were  gradually  introduced  to  these  alternations, 
and  that  selection  has  thus  had  an  opportunity  to  work  for  countless 
generations  in  producing  the  corresponding  complex  adaptations  and 
powers  of  accommodation.  It  may  be  granted  that  man  and  his 
ancestors  have  consumed  an  equal  succession  of  ages  in  attaining  the 
inherited  intellectual  constitution  that  fits  him  for  his  higher  sphere, 
without  lessening  our  apprehension  of  the  wonderful  contrast  between 
man  and  all  lower  organisms,  in  his  power  to  enter  suddenly  upon  a 
new  set  of  conditions.  This  power  is  so  great  that  man  may  suddenly 
enter  a  new  territory,  furnishing  not  a  single  product  that  he  can  eat, 
and  by  his  art  of  agriculture  so  completely  meet  his  needs  that  he 
becomes  a  permanent  settler  without  even  subjecting  himself  to  any 
new  form  of  selection.  In  other  words,  accommodation  is  in  some  cases 
so  complete  that  coincident  selection  is  prevented.  This  suggests  that 
in  some  spheres  of  activity,  coincident  {that  is,  organic)  selection,  is  less 
liable  to  occur  in  man  than  in  animals  whose  accommodation  is  less 
complete. 

8.  Endonomic  Selection  illustrated  by  Several  Species  0}  North  American  Birds. 

By  means  of  accommodation  birds  and  beasts  determine  their  rela- 
tions to  the  environment,  and  so  deter^nine  the  kind  of  selection  to  which 
they  and  their  descendants  are  thereafter  subjected.  The  choice  of  con- 
ditions that  have  brought  pleasant  experiences  and  the  avoidance 
of  those  that  have  brought  unpleasant  experiences  is  a  degree  of 
intelligence  enjoyed  by  many  species  of  animals,  and  is  a  form  of 
accommodation  that  may  determine  the  mode  of  life  and  so  deter- 
mine the  forms  of  selection.  For  example,  the  clifiF  swallow,  rang- 
ing over  most  of  North  America,  has  accommodated  itself  to  the  new 
conditions  introduced  during  the  past  two  centuries  by  the  occu- 
pation of  the  country  by  house-building  people.  Except  in  a  few  of 
the  Western  States,  where  the  population  is  sparse  and  the  houses 
few,  it  has  deserted  the  cliffs  and  taken  up  its  abode  under  the  eaves 
of  the  houses,  thus  bringing  itself  into  very  close  connection  with  man 
and  subjecting  itself  to  some  forms  of  selection  which  it  might  have 


64  THE   FOUR   SEGREGATIVR   PRINCIPLES. 

escaped  by  remaining  in  the  cliflfs.*  These  forms  of  selection  are  im- 
posed on  itself  by  the  forms  of  accommodation  the  species  has  assumed, 
for  the  conditions  are  not  so  determined  by  the  environment  that  no 
alternative  remains  to  the  organism.  The  cliff  swallow  might  still 
build  its  nest  in  the  cliff.  The  selection  to  which  it  is  exposed  is 
determined  by  the  choice  of  the  bird  between  alternatives  afforded  by 
the  environment,  and  may  therefore  be  called  endonomic  selection. 

9.  Endonomic  and  Coincident  Selection  Illustrated  by  the  Survival  of 
Infants  Fed  on  Substitutes  for  Mother's  Milk. 

Not  only  are  previous  forms  of  environal  selection  brought  to  an  end  by 
accommodation,  but  certain  forms  of  reflexive  selection  may  be  thus 
made  to  cease,  and  perhaps  other  forms  introduced.  From  the  era  when 
the  mammalian  class  first  arose  till  comparatively  recent  times,  every 
mammalian  mother  that  failed  to  give  milk  also  failed  of  raising  her 
young;  and  so  the  propagation  of  a  stock  seriously  deficient  in  this 
respect  was  rigorously  prevented  by  filio- parental  selection.  How- 
ever, amongst  human  mothers  such  cases  occasionally  arise;  and, 
amongst  civilized  races,  the  provision  for  the  young  thus  deprived  of 
their  natural  nourishment  is  so  complete  that  they  are  placed  at  no 
disadvantage.  This  form  of  filio-parental  selection,  which  has  been  in 
full  force  for  countless  ages,  now  ceases  for  civilized  man.  Among  half- 
civilized  races  the  substitutes  for  the  mother's  milk  vary  with  each 
nation,  and  the  original  filio-parental  selection  is  supplanted  by  a  form 
of  social  selection ;  for  the  article  used  as  a  substitute  is  determined 
by  tradition,  and  the  material  furnished  is  so  deficient  in  the  needed 
qualities  that  a  proportion  of  the  infants  are  unable  to  survive  on  such 
food.  The  survivors  are,  therefore,  determined  by  endonomic  selec- 
tion. They  are  selected  on  account  qf  their  being  better  endow^ed  for 
meeting  the  ordeal  of  feeding  on  the  substitute  provided  by  the  tra- 
dition of  the  community.  But  it  is  also  an  example  of  coincident  selec- 
tion ;  for  if  accommodation  had  not  come  in  to  aid  in  the  process  all 
infants  whose  mothers  failed  to  give  milk  would  have  perished.     On 


*  I  am  informed  by  Prof.  Lynds  Jones,  of  Oberlin  College,  that  several  birds  of 
North  America  have  passed  through  a  similar  transformation  of  their  habits. 
Besides  the  cliff  swallow  just  mentioned,  which  attaches  its  nest  to  the  overhang- 
ing eaves  of  a  house  instead  of  plastering  it  against  the  roof  of  a  cave  or  hole  in 
the  cliff,  there  is  the  barn  swallow,  which  usually  attaches  its  nest  to  the  rafter  of 
a  barn,  also  the  chimney  swift  (referred  to  in  the  early  part  of  this  sectioa),  that 
used  to  build  in  hollow  trees.  The  tree  swallow  and  the  house  wren  are  two 
species  that  are  still  in  a  transition  state  in  their  habits,  for  many  of  them  avail 
themselves  of  bird-boxes  or  of  holes  and  snug  nooks  about  houses,  while  others 
prefer  holes  in  trees  and  stumps,  as  in  better  accord  with  old  and  safe  traditions. 


ENDONOMIC    AND   COINCIDENT  SELECTION   CONTRASTED.  65 

Ponape,  one  of  the  Caroline  Islands,  the  only  substitute  for  mother's 
milk  known  to  the  aborigines  is  the  juice  that  exudes  from  the  imma- 
ture fruit-stalk  of  the  cocoanut  tree  when  the  end  of  the  immense  bud 
is  sliced  off.  In  Japan,  if  a  wet  nurse  can  not  be  provided,  sweet 
extract  of  malt  is  used.  In  some  lands  mare's  milk  is  used;  in  some 
ass's  milk;  and  in  others  goat's  milk,  or  cow's  milk;  but  all  these  are 
somewhat  deficient,  unless  modified  and  sterilized  by  the  highest  skill 
of  the  physiologist  and  chemist.  Any  case  of  selection  introduced  and 
protected  from  failure  by  accommodation  is  a  case  of  ''coincident  (or 
organic)  selection."* 

10.  Endonomic  Selection  and  Coincident  Selection  Contrasted. 

Active  (or  endonomic)  selection  is  due  to  powers  enabling  the  organ- 
ism to  deal  with  the  same  environment  in  different  ways.  This 
power  is  especially  manifest  when  the  organism  is  dealing  in  isolated 
groups  with  the  same  conditions.     Different  methods  arise : 

( 1 )  Because  the  innate  aptitudes  of  different  individuals  and  groups 
for  dealing  with  the  environment  differ  somewhat.  This  results  in 
aptitudinal  selection. 

(2)  Because  the  training,  and,  therefore,  the  habitudes,  of  different 
individuals  and  groups,  in  dealing  with  the  environment,  differ  some- 
what.    This  results  in  habitudinal  selection. 

(3)  Because  individuals  with  the  same  aptitudes  and  habitudes 
may  take  up  different  methods  of  dealing  with  the  same  environment, 
through  the  accidents  attending  their  entrance  on  their  new  districts, 
both  in  cases  when  these  new  districts  all  differ  from  the  original  home 
in  the  same  way  and  when  all  afford  exactly  the  same  conditions  as  the 
original  home.  Shall  we  call  this  accidental  selection  ?  Or  will  some 
one  suggest  some  other  term  more  suitable  ? 

Coincident  (or  organic)  selection  is  due  to  the  protection  derived 
from  the  discriminative  and  other  accommodational  powers  of  the 
individuals,  preserving  the  organism  from  extinction  under  the  stress 
of  great  and  sudden  change,  either  in  the  environment  or  in  the  rela- 
tions of  the  members  to  each  other,  and  thus  giving  time  for  the  pro- 
duction and  accumulation  of  variations  that  coincide  with  the  accom- 
modation in  adapting  the  organism  to  the  new  conditions. 

Active  (or  endonomic)  selection  rests  on  "alternative  methods  of 
adjustment  to  the  same  environment  till  the  organism  has  adopted  a 
particular  method  of  suiting  itself  to  its  conditions,  "'f 

*  See  Baldwin's  Development  and  Evolution,  pp.  95  and  173. 
t  This  form  of  statement  is  quoted  from  Headley's  Problems  of  Evolution,  p. 
149,  where  he  is  describing  what  he  calls  methods  of  evolution  by  natural  selection. 


66  THE   FOUR   SEGREGATIVE    PRINCIPLES. 

Coincident  selection  rests  on  the  protective  and,  therefore,  control- 
ling influence  of  accommodation  rather  than  adaptive  variation,  during 
several  generations  of  first  encounter  with  great  changes. 

11  .  Coincident  Election  Illustrated. 

Any  form  of  election  when  introduced  and  protected  from  failure  by 
variation  and  selection  I  call  "coincident  election."  A  ship  bearing  a 
number  of  families  of  Europeans  is  wrecked  on  an  island  of  the  cen- 
tral Pacific,  where  the  only  land  product  available  for  food  is  the 
cocoanut,  while  the  sea  is  swarming  with  fish,  sea-weeds,  crabs, 
shellfish,  etc.,  furnishing  a  large  variety  of  nourishment.  One-half 
of  the  shipwrecked  people  are  by  nature  fond  of  the  water  and  are 
able  to  secure  an  abundance  of  food.  The  others,  unable  to  swim 
and  dreading  the  sea,  seek  their  support  from  the  barren  land  and 
are  so  hard  pressed  for  food  that  most  of  them  perish,  while  some  of 
them  overcome  their  instincts  and  seek  food  from  the  sea,  though  at 
a  disadvantage  as  compared  with  those  who  are  at  home  in  the  water. 
In  time  the  arts  of  fishing,  and  swimming,  and  diving,  and  canoe 
building  and  navigating  are  so  fully  developed  that  a  thrifty  and  vig- 
orous colony  is  established,  in  which  the  type  of  election,  both  reflexive 
and  environal,  is  determined  by  the  relations  of  the  community  to  the 
sea.  But  these  relations  to  the  sea  were  made  possible  by  the  fact 
that  part  of  the  community  were  by  nature  endowed  with  some  meas- 
ure of  aptitude  for  such  a  life.  If  all  had  been  as  destitute  of  such 
aptitudes  as  a  colony  of  gorillas  the  whole  colony  would  have  per- 
ished, unless  perchance  a  few  might  have  led  a  precarious  existence, 
subsisting  entirely  on  cocoanuts.  Such  a  case  would  he  an  example  of 
coincident  election. 

12.  Endonomic  and  Coincident  Influences  Contrasted  and  Defined. 

Isolation,  selection,  partition,  and  election  are  controlled  by  endo- 
nomic influences  when  the  relations  of  the  group  to  the  environment 
are  liable  to  be  turned  in  different  directions  according  to  the  pre- 
viously attained  innate  aptitudes  or  acquired  habitudes  of  the  indi- 
viduals from  whom  the  colony  springs.  This  action  becomes  most 
manifest  when  the  isolated  sections  of  the  group  are  exposed  to  the 
same  environment  that  surrounds  the  original  stock ;  but  there  may 
also  be  alternative  methods  of  dealing  with  a  new  or  greatly  changed 
environment,  and  in  such  cases  endonomic  influences  are  present. 

If  inherited  aptitudes  are  the  controlling  influence  preceding  and 
shaping  the  habitudes,  then  the  partition  and  election  are  said  to  be 
coincident.  If  acquired  habits  and  other  powers  of  accommodation 
are  the  controlling  factors,  then  the  isolation  and  selection  are  said  to 


CATS  THAT  HAVE  LOST  AVERSION  TO  WADING  AND  SWIMMING.      67 

be  coincident.  It  therefore  follows  that  in  the  lower  forms  of  animal 
life  the  partition  and  election  is  largely  coincident,  while  in  the  case 
of  the  higher  animals,  and  especially  with  man,  the  powers  of  accom- 
modation being  the  leading  factors,  the  isolation  and  selection  are 
largely  coincident. 

Industrial  partition  brings  together,  in  the  mining  regions  of  Colo- 
rado, a  peculiar  type  of  people,  gathered  together  from  many  regions 
where  the  opportunities  for  exercising  their  special  training  are  not  as 
great  as  in  this  frontier  mining  region.  But  this  industrial  partition 
introduces  and  determines  industrial  isolation,  for  it  inevitably  leads 
to  the  segregate  propagation  of  the  peculiar  type  brought  together  in 
these  mining  regions;  and  this  industrial  isolation  thus  produced  is 
an  example  of  coincident  isolation. 

Active  (or  endonomic)  influences  are  due  to  the  fact  that  the 
species  may  use  alternative  methods.  The  number  of  alternative 
methods  of  dealing  with  the  environment  rests  upon  the  variety  of 
possible  choices  open  to  the  different  sections  of  a  species ;  and  this  is 
determined  by  the  variety  of  innate  aptitudes  and  of  acquired  habi- 
tudes, and  of  new  discriminative  experiments  that  the  species  can 
furnish. 

Coincident  influences  are  due  to  the  fact  that  adaptive  variations 
and  accommodations  may  cooperate  in  dealing  with  conditions  in 
a  harmonious  way.  When  variation  with  adaptation  prepares  the 
way  for  and  controls  innovation  with  accommodation,  we  have 
coincident  partition  and  election.  When  innovation  with  accommo- 
dation prepares  the  way  for  and  controls  variation  with  adaptation, 
we  have  coincident  isolation  and  selection. 

13    A  Colony  of  Cats  that  have  lost  Aversion  to  Wading  and  Swimming. 

The  interaction  of  the  principles  of  segregation  is  illustrated  by  the 
Tarpon  Island  cats.  One  of  the  most  decided  instincts  of  the  ordinary 
cat  is  to  avoid  immersion  in  water  or  any  other  liquid.  His  inherited 
nature  leads  him  to  dislike  to  wet  even  his  feet ;  but  there  may  arise 
conditions  under  which  he  will  use  his  paws  in  drawing  food  out  of  the 
water.  More  than  one  has  learned  to  help  himself  to  cream  placed  in 
an  open  jar  by  thrusting  his  paw  into  the  liquid  and  then  licking  off 
what  adheres.  Some  have  learned  to  skim  pans  of  milk  in  a  similar 
way,  and  others  have  become  adepts  in  fishing  for  goldfish  kept  in 
glass  globes  or  aquaria.  These  undoubted  examples  of  the  partial 
overcoming  of  their  natural  aversion  renders  it  easier  to  believe  the 
following  account  of  a  complete  change  of  habits  in  a  certain  isolated 
group  of  cats. 


68  THS   POUR   SKGRKGATIVE   PRINCIPIvRS. 

According  to  the  New  Orleans  Times- Democrat*  there  are  on  the 
shores  of  Louisiana,  near  the  mouth  of  the  Mississippi  river,  two  types 
of  cats.  The  great  majority  are  hke  the  cats  of  other  regions,  but  a 
small  tribe  on  Tarpon  Island  have  apparently  lost  all  aversion  to  being 
in  the  water.  Their  separation  from  other  families  of  cats  has  allowed 
of  their  establishing  their  habits  of  feeding  on  entirely  new  lines  of 
tradition,  for  they  all  wade  freely  in  the  shallow  waters  of  the  beach 
hunting  for  small  fish ;  and  three  or  four  of  the  bolder  ones  swim  off 
to  oyster  boats  lying  at  anchor  near  by.  This  is  an  example  of  parti- 
tion allowing  an  innovation  to  be  established  through  election  as  a 
permanent  habitude;  and  as  Captain  Bosco,  who  owns  these  cats, 
says  it  is  many  years  since  they  began  to  go  into  the  water,  we  have 
reason  to  believe  that  coincident  selection  has  begun  to  operate  in 
producing  a  breed  whose  innate  instincts  are  better  adapted  to  this 
mode  of  life  than  were  those  of  the  original  stock  from  which  they 
sprang;  or  may  it  not  be  possible  that  the  direct  inheritance  of  ac- 
quired characters  has  removed  the  instinctive  aversion  to  water  that 
belongs  so  universally  to  cats?  If,  now,  after  the  habits  and  innate 
instincts  of  the  new  breed  are  well  established,  several  pairs  of  them 
should  be  taken  to  a  part  of  the  shore  where  other  cats  possessing 
the  usual  instincts  of  the  species  are  found,  it  is  possible  that  their 
special  endowments  and  social  habits  might  lead  them  to  associate 
with  each  other,  and  thus  to  perpetuate  the  habits  alreadv  formed, 
and  to  breed  with  each  other.  If  such  should  be  the  case,  it  would  be 
an  example  of  social  and  industrial  partition,  leading  to  discriminate 
isolation  and  tending  to  produce  permanent  segregate  breeding.  As, 
however,  the  segregative  social  instincts  of  the  cat  seem  to  be  weak 
compared  with  those  of  most  mammals,  the  opportunity  for  establish- 
ing separate  races  of  cats  is  not  as  good  as  in  the  case  of  most  domestic 
species. 

14.   Cooperation  oj  Structural  Isolation  and  Structural  Selection  Illustrated. 

The  correlation  that  may  exist  between  a  given  form  of  isolation  and 
the  corresponding  form  of  selection  is  seen  in  the  case  of  the  different 
forms  of  impregnational  isolation  and  impregnational  selection.  Let 
us  consider  the  case  of  two  varieties  of  the  same  species  of  land  snails 
that  are  prevented  from  crossing  by  the  fact  that  in  one  variety  the 
sexual  organs  are  on  the  right  side  of  the  body  (the  male  organs 
being  near  the  head  and  the  female  organs  a  little  further  back), 
while  in  the  other  variety  they  are  arranged  in  the  same  way  on  the 


*  New  Orleans  Times- Democrat,  probably  January,  1900,  as  it  was  copied  by  a 
Philadelphia  paper  late  in  January,  1900. 


STRUCTURAL   ISOLATION  AND  STRUCTURAL  SELECTION.  69 

left  side  of  the  body.  The  first  is  called  a  dextral  variety,  and  bears 
a  dextral  shell.  Each  individual  has  both  male  and  female  organs, 
and  any  two  dextral  individuals  easily  unite  and  impregnate  each 
other,  as  do  also  any  two  sinistral  individuals.  But  if  a  dextral 
individual  and  a  sinistral  are  brought  together,  I  think  it  will  prove 
impossible  for  them  to  impregnate  each  other  owing  to  the  lack  of 
correlation  in  their  forms.  I  earnestly  hope  that  in  the  Hawaiian 
Islands,  where  there  are  not  a  few  species  represented  by  both  dextral 
and  sinistral  varieties,  careful  investigation  of  this  point  will  be  made. 

I  anticipate  that  crossing  between  dextral  and  sinistral  forms  will 
be  found  to  be  impossible.  If  this  is  so,  it  is  probable  that  if,  in  a 
group  of  one  form  occupying  one  tree,  there  arise  in  the  same  genera- 
tion two  or  more  individuals  of  the  reverse  form  from  the  original 
stock,  they  will  mate;  and  there  will  be  formed,  without  intergrading 
steps,  a  completely  segregated  group,  determined  in  the  first  place  by 
structural  isolation.  It  should,  however,  be  noted  that  when  the  rep- 
resentatives of  any  species  found  on  any  one  tree  are  all  either  dextral 
or  sinistral,  any  single  individual  of  the  reverse  form  that  may  appear 
in  any  generation  will  be  prevented  from  leaving  offspring,  and  the 
result  will  be  structural  selection,  a  form  of  reflexive  selection  deter- 
mined by  and  cooperating  with  structural  isolation. 

Let  us  now  consider  whether  environal  selection  is  one  of  the  causes 
that  produces  both  dextral  and  sinistral  varieties  occupying  the  same 
valley  and  often  sharing  the  same  groves  or  the  "same  individual 
trees,  and  for  the  sake  of  definiteness  let  us  suppose  that  the  original 
form  entering  the  valley  was  dextral.     We  then  ask : 

(i)  Did  the  two  or  more  sinistral  individuals  originating  the  new 
type  gain  any  advantage  from  their  sinistral  form  when  they  first 
appeared? 

(2)  Does  the  colony  as  it  now  exists  derive  any  advantage  from 
their  form  that  they  would  not  equally  enjoy  if  they  had  all  remained 
in  the  original  dextral  form? 

(3)  If  a  colony  of  sinistral  individuals  occupying  a  given  candlenut 
tree  and  a  colony  of  dextral  individuals  occupying  another  tree  of  the 
same  species  are  made  to  exchange  trees,  will  each  group  find  them- 
selves unfitted  for  the  new  position  ? 

My  observations  on  dextral  and  sinistral  varieties  of  Hawaiian  snails 
lead  me  to  believe  that  in  every  case  all  three  of  these  questions 
should  be  answered  in  the  negative ;  and  that,  therefore,  the  forma- 
tion of  this  distinction  can  not  be  attributed  to  natural  selection,  nor, 
indeed,  primarily  to  any  form  of  selection.  After  the  new  form  has 
been  produced  by  variation  and    preserved  by  structural  isolation, 


70  THE   FOUR   SEGREGATIVE   PRINCIPLES. 

structural  selection  may  cooperate  in  maintaining  the  same ;  but  the 
new  form  of  selection  is  entirely  dependent  on  the  isolation  which  has 
opened  the  way  and  partially  established  the  new  form. 

The  production  of  a  sinistral  form  by  a  dextral  species,  or  of  a  dex- 
tral  form  by  a  sinistral  species,  is  a  striking  example  of  what  De  Vries 
calls  mutation.*  Undoubtedly  new  forms  have  sometimes  arisen  in 
this  sudden  way  and  have  been  continuously  propagated  without  the 
aid  of  man  in  securing  artificial  segregation.  But  that  it  is  the  exclu- 
sive or  even  the  predominant  method  by  which  divergence  of  species 
takes  place  has  not  been  shown.  In  the  case  of  sinistral  snails  the 
question  naturally  arises  whether  there  are  certain  habits  of  life  that 
favor  this  form.  Can  any  reason  be  found  why  this  form  is  much 
more  common  among  those  groups  of  species  that  are  entirely  arboreal 
in  their  habits  than  among  those  that  live  on  the  ground?  Does  the 
position  assumed  by  those  that  cling  to  the  underside  of  branches,  or 
to  the  perpendicular  trunks  of  trees,  facilitate  the  production  of 
young  of  the  sinistral  form? 

15.  Some  Young  Snails  have  the  Reverse  Coil  from  that  oj  their  Parents. 

Since  writing  the  above,  my  attention  has  been  called  to  the  follow- 
ing statement  by  Dr.  A.  G.  Mayer, f  concerning  certain  species  of 
Partula  found  on  the  island  of  Tahiti : 

The  young  of  dextral  or  sinistral  snails  are  usually  dextral  or  sinistral  respec- 
tively, but  this  is  not  invariably  the  case.  It  is  interesting  to  observe,  however, 
that  all  of  the  young  developed  within  any  given  adult  [at  the  same  time]  are 
either  dextral  or  sinistral,  never  some  of  them  dextral  and  others  sinistral.  The 
young  are  born  one  at  a  time,  three  eggs  and  two  or  three  young  snails  in  various 
stages  of  development  being  often  found  in  a  single  adult  animal. 

This  seems  to  indicate  that  the  causes  producing  in  the  young  a 
reversed  coil  from  that  in  the  parent  operate  alike  on  each  embryo 
within  the  parent  at  the  same  time,  and  are  likely  to  produce  more  than 
one  individual  of  the  reversed  form  when  any  are  produced,  and  so 
to  open  the  way  for  a  new  racial  type,  which  we  have  reason  to  believe 
is  completely  segregated  from  the  original  type,  though  both  occupy 
the  same  valley,  or  even  the  same  tree. 


♦An  interesting  article  on  "The  Origin  of  Species,"  by  De  Vries,  translated 
from  "Album  der  Nature,"  and  revised  by  the  author,  will  be  found  in  the  Pop- 
ular Science  Monthly  for  April,  1903.  See  also  an  article  by  the  same  author  in 
Harper's  Magazine  for  January,  1905. 

t  Memoirs  of  the  Museum  of  Comparative  Zoology  at  Harvard  College,  Vol 
XXVI,  No.  2,  pp.  121,  122. 


MUTATIONS  AND  VARIETIES.  7 1 


16.   Mutations  and  Varieties. 

In  a  recent  volume  by  Prof.  T.  H.  Morgan  (Evolution  and 
Adaptation,  1903)  we  find  an  interesting  exposition  of  the  mutation 
theory,  from  which  we  quote  a  few  sentences : 

Amongst  the  mammalia  and  birds  of  North  America  there  are  many  cases  of 
local  forms  or  races,  some  of  which  at  least  are  probably  mutations.  This  can 
only  be  proven,  however,  by  actually  transferring  the  forms  to  new  localities  in 
order  to  find  out  if  they  retain  their  original  characters  or  become  changed  into 
another  form  [p.  292].  As  De  Vries  has  pointed  out,  each  mutation  may  be  differ- 
ent from  the  parent  form  in  only  a  slight  degree  for  each  point,  although  all  the 
points  may  be  different.  The  most  unique  feature  of  these  mutations  is  the  con- 
stancy with  which  the  new  form  is  inherited.  *  *  *  There  is  another  point 
of  great  interest  in  this  connection.  Many  of  the  groups  that  Darwin  recognized 
as  varieties  correspond  to  the  elementary  species  of  De  Vries.  These  .varieties, 
Darwin  thought,  are  the  first  stages  in  the  formation  of  species,  and,  in  fact,  can 
not  be  separated  from  species  in  most  cases.  The  main  difference  between  the 
selection  theory  and  the  mutation  theory  is  that  the  one  supposes  tliese  varieties 
to  arise  through  selection  of  individual  variations,  the  other  supposes  that  they 
have  arisen  spontaneously  and  at  once  from  the  original  form.  The  development 
of  these  varieties  into  new  species  is  again  supposed,  on  the  Darwinian  theory,  to 
be  the  result  of  further  selection;  on  the  mutation  theory,  the  result  of  the  appear- 
ance of  new  mutations.  *  *  *  Some  of  the  advantages  of  the  mutation 
theory  may  be  briefly  mentioned  here. 

1.  Since  the  mutations  appear  fully  formed  from  the  beginning,  there  is  no 
difficulty  in  accounting  for  the  incipient  stages  in  the  development  of  an  organ, 
and  since  the  organ  may  persist,  even  when  it  has  no  value  to  the  race,  it  may 
become  further  developed  by  later  mutations,  and  may  come  to  have  finally  an 
important  relation  to  the  life  of  the  individual. 

2.  The  new  mutations  may  appear  in  large  numbers,  *  *  *  and  the  dan- 
ger of  becoming  swamped  through  crossing  with  the  original  form  will  be  lessened 
in  proportion  to  the  number  of  new  individuals  that  arise. 

3.  If  the  time  of  reaching  maturity  in  the  new  form  is  different  from  that  in  the 
parent  form,  then  the  new  species  will  be  kept  from  crossing  with  the  parent  form, 
and  since  this  new  character  will  be  present  from  the  beginning,  the  new  form  will 
have  much  better  chances  of  surviving  than  if  a  difference  in  time  of  reaching  ma- 
turity had  to  be  gradually  acquired. 

4.  The  new  species  may  be  in  some  cases  already  adapted  to  live  in  a  different 
environment.     *     *     *     and  so  will  be  isolated  from  the  beginning.     *     *     * 

5.  It  is  well  known  that  the  difference  between  related  species  consists  largely 
in  differences  of  unimportant  organs,  and  this  is  in  harmony  with  the  mutation 
theory,  but  one  of  the  real  difficulties  of  the  selection  theory. 

6.  Useless  or  even  slightly  injurious  characters  may  appear  as  mutations,  and 
if  they  do  not  seriously  affect  the  perpetuation  of  the  race,  they  may  persist  (pp. 
297-299). 


72  THE   POUR   SEGREGATIVE   PRINCIPLES. 

17.  Theories  Compared. 

It  will  be  observed  that  in  the  above-quoted  statements  recognition 
is  given  to  the  following  facts,  to  which  attention  was  called  in  the 
papers  reproduced  in  the  Appendix  of  the  present  volume. 

(i)  That  there  may  be  divergent  varieties  that  are  not  produced 
by  exposure  to  different  environments. 

(2)  That  these  varieties  are  often  local. 

(3)  That  when  isolated  the  peculiar  character  of  the  variety  is  not 
swamped  by  crossing. 

(4)  That  these  varieties  may  be  so  accumulated  as  to  produce  di- 
vergent species,  whose  differences  are  not  due  to  differences  in  the 
environment. 

(5)  That  the  differences  found  in  allied  varieties  and  species  are 
often  differences  that  are  not  necessary  for  the  survival  of  the  different 
groups. 

This  series  of  important  facts  that  have  been  either  overlooked  or 
assumed  to  be  impossible  by  a  leading  school  of  evolutionists  are,  I 
believe,  fully  recognized  by  the  expounders  of  the  mutation  theory, 
though  it  seems  to  me  that  a  fuller  explanation  may  be  given  than  any 
they  have  offered.  It  seems  to  me  that  both  the  Darwinian  theory  and 
the  mutation  theory  are  lacking  in  that  they  have  not  given  sufficient 
attention  to  the  influence  of  isolation,  first  in  protecting  divergent 
types,  whether  great  or  small,  second  in  cutting  off  all  community  of 
action  in  the  different  forms  of  reflexive  selection,  and  third  in  open- 
ing the  way  for  diversity  of  environal  selection,  through  diversity  in 
the  methods  of  dealing  with  the  environment.  They  have  also  failed 
of  recognizing  that  this  controlling  influence,  arising  from  methods  of 
using  the  environment,  and  leading  to  increasing  divergence  in  suc- 
ceeding generations,  may  find  its  starting  point  in  the  individual  pe- 
culiarities of  the  founders  of  the  colony,  whether  these  peculiarities 
be  inherited  aptitudes  or  acquired  habitudes.  The  Darwinian  theory 
is  deficient  in  that  it  has  no  explanation  of  the  divergent  evolution  of 
two  isolated  groups  of  the  same  species  exposed  to  the  same  environ- 
ment. The  mutation  theory  recognizes  that  the  individuals  starting 
one  colony  may  happen  to  be  of  a  different  mutation  from  those  form- 
ing the  other  colony,  and  that,  therefore,  the  colonies  may  be  different 
from  the  first  generation ;  but  it  fails  to  give  any  explanation  of  why 
they  should  become  increasingly  divergent  in  the  generations  that 
follow.  In  opposition  to  the  Darwinian  theory,  it  denies  that  any 
permanent  effect  can  be  produced  by  the  selection  of  individual 
variations,  and,  therefore,  if  two  pairs  of  individuals  belonging  to  the 


DEGENERATION  THROUGH  SURVIVAL  O^  INFERIOR  INDIVIDUALS.    73 

same  mutation  should  become  the  parents  of  two  isolated  colonies,  it 
ought  to  predict  that  every  variation  occurring  in  either  colony  will  . 
be  found  in  both,  and  in  the  same  proportion.     That  this  will  be  the 
case  has  not  yet  been  shown. 

Without  variation  in  its  different  forms  cooperating  with  heredity, 
isolation  and  selection  could  have  no  influence  in  guiding  and  shaping 
evolution.  It  is,  therefore,  well  that  the  mutation  theory  insists  on  the 
importance  of  these  fundamental  factors  and  of  the  laws  by  which 
they  are  controlled.  But  it  must  be  remembered  that  through  the 
powers  of  variation  and  heredity  the  principles  of  free  crossing,  isola- 
tion, and  selection  gain  profound  significance.  These  latter  are  the 
conditions  through  which  the  laws  of  the  fundamental  factors  are 
revealed ;  and  if  we  misinterpret  the  laws  we  shall  fail  in  our  explana- 
tion of  the  process.  These  laws  have  not  been  fully  brought  to  light ; 
but  is  there  no  reason  to  suspect  that  there  is  something  lacking  in 
the  theory  that  the  selection  of  individual  variations  can  have  no 
effect  on  the  final  result  ?  * 

18.  Degeneration  of  Species  when  the  Standard  of  Survival  is  lowered. 

The  frequently  observed  fact  that  characters  built  up  by  the  arti- 
ficial selection  of  individual  variations  gradually  disappear  when  the 
selection  entirely  ceases  seems  to  be  the  chief  reason  for  disregarding 
the  influence  of  such  variations  in  the  formation  of  varieties  and 
species.  But  is  not  the  same  tendency  seen  in  the  characters  of  nat- 
ural species  which  the  mutation  theory  assumes  to  have  resulted  from 
mutations?  Are  there  not  characters  that  have  been  maintained 
with  unbroken  constancy  through  countless  generations  of  ancestors, 
not  only  through  all  the  past  history  of  the  present  species,  but 
through  the  much  longer  history  of  many  ancestral  species,  and  that 
yet  do  not  reach,  in  every  individual  of  the  species,  the  standard  neces- 
sary for  survival  ?  If  such  individuals  are  able  to  escape  the  fate  that 
has  overtaken  similarly  defective  ones  of  previous  generations  they 
will  help  to  lower  the  standard  of  attainment  previously  gained  by 
the  species  to  which  they  belong.  This  process  may  be  repeated  in 
successive  generations  till  the  character  is  entirely  lost.  Different 
stages  of  such  a  process  are  revealed  in  the  present  condition  of  cer- 
tain species  of  birds,  in  regard  to  the  instinct  that  leads  the  mother 
bird  to  sit  on  the  eggs  she  lays,  and  to  provide  for  the  young  when 

*  Prof.  T.  H.  Morgan's  position  is  seen  in  the  following  statement:  "Nature's 
supreme  test  is  survival.  She  makes  new  forms  to  bring  them  to  this  test  through 
mutation,  and  does  not  remodel  old  forms  through  a  process  of  individual  selec- 
tion."    See  "Evolution  and  Adaptation,"  p.  464. 


74  THE   FOUR   SEGREGATIVE   PRINCIPLES. 

they  appear.  The  American  cowbird  and  the  Enghsh  cuckoo  seem 
to  have  entirely  lost  the  instinct.  Again,  the  physiological  power  of 
the  mammalian  mother  to  provide  milk  for  her  young  seems  to  be 
gradually  declining  in  the  human  species,  through  the  survival  and 
propagation  of  the  children  of  mothers  presenting  individual  varia- 
tions below  the  standard  that  for  countless  generations  was  necessary 
in  order  to  leave  descendants.  If  statistical  investigation  should 
show  that  lack  of  sufhcient  milk  for  their  young  is  most  common  in 
mothers  belonging  to  communities  that  have  for  the  longest  time,  and 
most  successfully,  met  every  deficiency  of  this  kind,  it  would  be  a 
strong  indication  that  the  accumulation  of  individual  variations  can 
not  be  overlooked  in  a  complete  theory  of  the  factors  of  evolution. 

19.  Degeneration  in  Eyesight  and  its  Lessons. 

Another  example  of  a  similar  kind  is  found  in  the  power  of  sight  in 
mankind.  I  believe  it  is  fully  recognized  that  in  civilized  races  the 
proportion  of  individuals  with  defective  sight  is  much  greater  than  in 
savage  races;  and  the  best  explanation  that  has  been  given  is  found 
in  the  equally  certain  fact  that  with  civilized  man  the  standard  of 
sight  necessary  for  individual  survival  has  been  reduced  to  zero,  and 
the  standard  necessary  for  attaining  the  highest  prosperity  and  the 
fullest  share  in  the  propagation  of  the  race  is  far  below  that  which  is 
necessary  among  savages.  Is  there  any  reason  to  doubt  that  the  dif- 
ference in  the  average  inherited  power  of  vision  in  the  two  cases  is 
due  to  the  fact  that  for  many  generations  individual  savages  with 
deficient  sight  have  had  less  opportunity  for  leaving  descendants 
than  have  individuals  with  the  same  deficiency  belonging  to  civilized 
races?  Without  the  selection  of  individual  variations  in  the  primitive 
races  of  man,  the  power  of  these  races  would  have  fallen  so  low  that 
the  species  would  have  been  exterminated  in  its  conflict  with  other 
species.  But  the  survival  of  man,  due  to  this  selection  of  individual 
variations,  is  in  no  small  degree  determining  what  other  species  shall 
survive;  and  the  determination  of  the  species  that  survive  controls 
the  types  of  the  mutations  that  from  time  to  time  appear,  and  would, 
therefore,  control  the  types  of  future  species,  even  if  every  such  new 
form  must  find  its  origin  in  a  mutation. 

First  Lesson. — It  therefore  seems  to  be  shown  that  the  accumula- 
tion of  individual  variations  by  selective  generation  has  had,  and 
must  continue  to  have,  a  profound  influence  on  the  course  of  evolu- 
tion; for,  if  the  selection  of  individual  variations  has  significance  in 
the  survival  of  species  in  one  period,  it  must  have  significance  in  the 
origin  of  species  in  the  periods  that  follow.     The  sinistral  mutations 


DEGENERATION    IN    BREEDING   INSTINCTS.  75 

produced  by  the  Helix  are  different  from  those  produced  by  the  Acha- 
tinella.  The  short-legged  lamb,  from  which  sprang  the  Ancon  sheep, 
was  not  the  suckling  of  a  lioness,  but  had  a  sheep  for  its  dam.  In 
other  words,  the  segregations  and  survivals  of  one  generation  control 
the  types  of  heredity  and  variation  (including  mutation)  in  the  next 
generation. 

Second  Lesson. — If  the  selection  of  individual  variations  is  necessary 
for  the  maintenance  of  the  normal  standard  of  eyesight  in  the  human 
species,  is  it  not  possible  that  the  same  necessity  exists  in  other 
species?  And  may  it  not  be  true  that  many  other  inherited  endow- 
ments are  subject  to  gradual  decay  when  the  standard  of  selection  is 
lowered?  If  we  find,  in  a  given  country,  that  the  mothers  who  have 
to  feed  their  babes  on  artificial  substitutes  for  mother's  milk  lose  a 
larger  per  cent  of  their  children  than  do  those  who  are  able  to  give 
suck,  does  it  necessarily  follow  that  the  power  of  giving  suck  is  in- 
creasing from  generation  to  generation  among  the  people  of  that 
country?  In  the  language  of  the  statistical  method,  is  it  not  possible 
that  the  "skewness"  of  the  "frequency  curve"  (for  different  grades 
in  the  power  of  furnishing  milk)  might,  in  such  a  case,  give  some 
indication  of  the  selection  that  is  taking  place,  and  that,  at  the  same 
time,  the  statistics  of  successive  generations  might  show  that  there 
was  no  gain  in  the  power?  Or,  in  such  a  case,  would  there  be  no 
skewness  in  the  frequency  curve,  though  there  is  constant  selection 
that  results  in  the  maintenance  of  a  constant  standard  ? 

20.  Degeneration  in  Breeding  Instincts. 

In  the  case  of  the  Old  World  cuckoo  it  may  be  a  question  whether 
the  loss  of  the  maternal  instinct  (or  rather  of  this  series  of  instincts), 
came  in  a  single  generation,  by  one  mutation,  maintaining  its  type 
with  constancy  from  the  first;  or  by  several  successive  mutations, 
each  mutation  being  added  to  the  previous  ones,  and  being  persist- 
ently inherited;  or  whether  the  process  has  been  a  very  gradual  ac- 
cumulation of  individual  tendencies  through  the  success  of  aberrant 
individuals  in  leaving  descent,  and  so  lowering  the  general  standard 
of  service  for  the  whole  species.  There  are,  however,  certain  facts 
that  point  toward  the  last  of  these  as  the  process  by  which  the  degen- 
eration has  taken  place.  F.  M.  Chapman,  in  his  Handbook  of  Birds 
of  Eastern  North  America,  notes  that  ' '  Many  species  [of  cuckoo]  are 
remarkable  for  the  irregularity  of  their  breeding  habits."  Of  the 
Ani,  a  genus  of  the  same  family,  he  says :  "The  Anis  are  communistic, 
and  build  but  one  nest,  in  which  several  females  lay  and  share  the 
task  of  incubation."     Now,  it  is  manifest  that,  in  a  community  of  this 


76  THB   FOUR   SEGREGATIVE    PRINCIPLES. 

kind,  one  mother-bird  might  fail  of  doing  her  share  of  the  task  of 
incubation  or  of  feeding  the  young,  and  still  be  represented  by  de- 
scendants, a  result  that  would,  in  the  next  generation,  slightly  lower 
the  average  standard  in  the  instincts  that  secure  faithful  service. 
Man  may  perhaps  be  able  to  devise  more  than  one  method  of  fore- 
stalling the  degeneracy  that  tends  to  arise  from  communal  methods 
of  providing  for  the  young;  but  for  the  simple-minded  Ani  there 
would  seem  to  be  no  possible  way  by  which  it  may  prevent  the  slowly 
increasing  decay  of  parental  instincts.  The  probability  is  that  in  the 
course  of  a  few  hundred  generations  the  cooperative  method  of  incu- 
bation and  of  providing  for  the  young  will  break  down  through  the 
general  tendency  to  shirk  the  task;  and  the  more  degenerate  mem- 
bers, who  have  heretofore  imposed  on  their  own  kindred,  will  find  it 
equally  easy  to  lay  their  eggs  in  the  nests  of  other  species  and  so  estab- 
lish the  method  that  has  already  been  reached  by  at  least  two  species. 

I  am  informed  by  Prof.  Lynds  Jones  of  an  irregularity  in  the  habit 
of  two  species  of  American  cuckoos  which  may  throw  some  light  on 
the  possible  steps  by  which  the  greater  degeneracy  of  the  Old  World 
cuckoo  has  been  reached.  The  yellow-billed  cuckoo  and  the  black- 
billed  cuckoo  are  clearly  marked  species,  both  found  nesting  in 
Eastern  North  America.  Usually  a  nest  of  either  species  contains 
only  the  eggs  or  young  of  that  species,  but  occasionally  an  interloper 
of  the  other  species  is  found.  If  a  delinquent  individual  of  either  of 
these  species  sometimes  lays  an  egg  in  the  nest  of  another  species,  is 
it  not  probable  that  it  has  failed  to  build  any  nest  of  its  own  and  is 
leaving  all  its  eggs  for  the  season  to  the  care  of  other  birds,  usually 
laying  them  in  the  nests  of  birds  of  the  same  species  and  thus  escaping 
the  inquisitive  impertinence  of  the  ornithologist,  who  finds  the  eggs 
all  of  one  color,  and  passes  without  suspicion?  At  any  rate,  the  faith- 
ful workers  of  the  species  seem  to  have  no  method  of  dealing  with  the 
delinquents  or  of  preventing  the  blending  of  their  descendants  with 
the  descendants  of  the  faithful.  There  is,  therefore,  some  reason  to 
fear  that  these  two  species  have  entered  on  a  path  that  will  lead  to 
extinction,  unless,  like  the  Old  World  cuckoo,  they  succeed  in  shifting 
the  work  of  raising  their  young  ones  on  to  other  species  of  more  sturdy 
instincts. 

Whether  the  change  in  the  Old  World  cuckoo  came  by  sudden 
mutation  or  by  gradual  accumulation  of  individual  variations,  it  was 
certainly  a  regressive  process,  undoing  instincts  that  had  been  inheri- 
ted for  countless  generations. 


MUTATION   AS   RECENTLY  EXPOUNDED   BY   DE   VRIES.  ^^ 

21 .  Mutation  as  recently  expounded  by  De  Vries. 

As  "Species  and  Varieties,  Their  Origin  by  Mutation,"  by  De  Vries, 
1905,  has  appeared  while  the  present  volume  is  being  put  into  type,  I 
add  a  few  words  on  the  very  interesting  experiments  there  described. 
In  his  first  lecture  he  fully  endorses  Morgan's  interpretation  of  the 
mutation  theory  and  speaks  of  the  lectures  that  are  to  follow  as  "a 
review  of  the  facts  obtained  from  plants  which  go  to  prove  the  asser- 
tion that  species  and  varieties  have  originated  by  mutation,  and  are, 
at  present,  not  known  to  originate  in  any  other  way."  (See  p.  9.) 
The  experiments  described  in  Lecture  XIX  show  that  Lamarck's 
evening  primrose,  as  it  now  exists  in  Holland,  is  subject  to  mutation ; 
for  over  two  per  cent  of  the  seed  taken  without  selection  from  plants 
that  have  been  grown  without  crossing  and  in  rich  soil  for  two  or  three 
generations,  produce  clearly  marked  digressions  from  the  original 
stock.  About  half  of  these  mutations  produce  the  variety  with  ob- 
long leaves,  while  the  remaining  half  produce  several  other  types. 
(See  p.  556.)  In  all,  twelve  new  types  have  been  observed,  of  which 
nine  are  entirely  constant  as  long  as  they  are  kept  isolated,  and  three, 
though  kept  unmixed,  produce  both  the  original  type  of  the  species 
and  the  new  type.  His  record  indicates  that  selection  has  not  been 
used  in  producing  these  results ;  but  how  different  are  the  facts  given 
in  the  production  of  the  double-flower  variety  of  the  corn-marigold. 
His  description  indicates  that  careful  selection,  during  successive 
generations,  of  seed  from  flowers  furnishing  the  largest  number  of 
ray  florets  brought  the  average  number  of  these  rays  up  to  2 1  in  the 
third  generation,  to  34  in  the  sixth,  to  47  in  the  eighth,  and  to  55  in 
the  ninth  generation.  In  the  seventh  generation  three  heads  were 
produced  with  a  few  rays  in  the  midst  of  the  disk;  in  the  eighth 
generation  the  maximum  number  of  rays  (counting  both  internal 
and  external  ones)  was  100,  in  the  ninth  generation  200.  "All  the 
children  of  this  original  mutated  plant  [the  plant  producing  the  three 
heads  just  mentioned]  showed  the  new  character.  *  *  *  ]sjot 
on  all  the  heads,  not  even  on  the  majority  of  the  heads  on  some 
individuals,  but  on  some  heads  all  gave  clear  proof  of  the  possession 
of  the  new  attribute."  (See  p.  504.)  My  only  suggestion  is  that 
since  the  selection  of  fluctuating  variations  for  six  generations  was 
necessary  in  order  to  reach  the  new  character  which  is  called  a 
mutation,  and  for  three  more  generations  in  order  to  perfect  the 
type,  selection  should  be  regarded  as  a  part  of  the  process  produc- 
ing the  new  type.  On  pages  468-478  he  describes  another  experi- 
ment with  another  species,  commencing  with  successive  selections  of 


78  THE  FOUR  PRINCIPLES  OF  SEGREGATION. 

fluctuating  variations  and  culminating  In  a  mutation  that  becomes 
stable. 

22.   Selection  and  the  Inheritance  of  Acquired  Characters. 

The  inheritance  of  functional  variation,  if  proved  in  any  case,  does  not 
prove  that  selection  has  had  no  influence  in  shaping  the  characters  of  the 
same  species.  In  a  recent  volume  by  J.  T.  Cunningham,  entitled 
"Sexual  Dimorphism,"  a  large  collection  of  very  interesting  facts  on 
the  subject  of  secondary  sexual  characters  has  been  presented.  It, 
however,  seems  to  me  that  but  little  proof  has  been  given  of  his  con- 
tention that  these  characters  have  been  produced,  not  by  selection, 
but  by  the  action  of  direct  stimulation  on  the  individual,  facilitated 
and  strengthened  in  successive  generations  by  an  increasing  inher- 
itance of  the  effects  of  stimulus  in  previous  generations.  Whether 
acquired  {i.  e.,  functional)  characters  and  tendencies  can  be  inherited 
demands  most  careful  investigation ;  but  if  it  is  found  to  be  a  fact  it 
will  not  disprove  the  importance  of  the  different  forms  of  selection  in 
determining  the  special  kinds  of  response  that  the  function  awakens. 
Hertwig  is  undoubtedly  right  when  he  says  that  neither  selection  nor 
the  inheritance  of  functional  variations  determines  whether  a  given 
bee's  egg  shall  develop  into  a  drone,  a  queen,  or  a  worker,  for  the 
determining  influence  is  the  power  of  responding  in  different  ways  to 
different  conditions.  The  question,  however,  remains  as  to  why  the 
workers  of  the  Italian  bee  develop  in  such  a  way  as  to  produce  a  long 
tongue,  while  certain  other  bees  develop  a  comparatively  short  tongue. 
Hertwig  admits  that  selection  has  had  much  to  do  with  this  diversity 
in  the  powers  of  response. 

In  Prof.  C.  B.  Davenport's  two  volumes  on  "Experimental  Mor- 
phology," a  large  mass  of  facts  illustrating  the  different  responses  of 
organisms  to  external  conditions  has  been  brought  together,  and  in 
certain  cases  the  effects  are  found  to  increase  in  successive  generations 
when  there  is  reason  to  believe  that  the  increase  is  not  due  to  selection. 
Though  the  inheritance  of  acquired  characters  may  be  proved  by 
these  experiments,  I  judge  that  Professor  Davenport  does  not  doubt 
that  the  different  forms  of  selection  have  an  important  influence  in 
shaping  the  specific  characters  of  the  same  organisms. 


CHAPTER  VI. 

ANALYSIS  OF  THE  FOUR  PRINCIPLES  OF  SEGREGATION,  WITH 

ILLUSTRATIONS. 

I.     Chief  Divisions  of  the  Four  Principles. 

1 .  Six  Conditions  on  which  the  Racial  Evolution  of  a  Cross-Fertilizing 
Group  must  rest. 

Before  we  proceed  further  with  the  analysis  of  the  principles  pro- 
ducing segregation,  we  shall  enumerate  certain  vital  conditions  which 
must  be  constantly  present  in  order  that  there  should  be  any  divergent 
evolution  in  allogamic  (t.  e.,  cross-fertilizing)  organisms.  Besides 
individual  assimilation  and  growth  there  must  be,  first,  the  power  of 
reproduction ;  second,  survival  (that  is,  the  number  and  adaptations 
of  individuals  produced  by  members  of  the  group  must  be  sufficient  to 
meet  the  losses  through  death  in  the  struggle  for  life),  for  otherwise 
the  group  will  be  exterminated;  third,  variation  (that  is,  tentative 
diversity  in  individual  innate  characters  and  aptitudes) ;  fourth, 
heredity  (that  is,  the  reproduction  of  fundamental  racial  characters) , 
and,  therefore,  the  continuance  of  types ;  fifth,  free  crossing  between 
the  males  and  females  of  the  different  variations  of  any  one  group ; 
sixth,  segregate  intergeneration  (that  is,  the  breeding  of  like  with 
like),  setting  limits  to  the  sphere  of  free  crossing,  and  so  controlling 
variation  and  heredity.* 


*  It  will  be  observed  that  I  regard  heredity  as  one  of  the  fundamental  powers 
on  which  the  evolution  of  organisms  depends.  If  there  were  no  heredity  a  proto- 
zoa might,  in  one  generation,  produce  the  highest  as  well  as  the  lowest  types  of 
organic  life;  an  elephant  might  be  the  father  of  a  mouse,  and  a  cabbage  might  be 
the  mother  of  a  rational  child.  The  importance  of  variation  in  the  process  of 
evolution  can  not  be  overstated;  but  there  can  be  no  variation  except  as  there  is 
a  type  from  which  the  variation  departs,  and  heredity  is  the  maintenance  with 
more  or  less  exactness  of  the  ancestral  type.  This  being  so,  it  seems  impossible 
to  accept  Prof.  H.  S.  William's  theory  that  "Variation,  and  not  heredity,  is  the 
fundamental  characteristic  of  the  phenomena  of  organisms."  (See  article  on 
"Variation  versus  Heredity ,"  American  Naturalist  for  1898,  p.  831.)  In  this  case, 
as  in  many  others,  the  propositions  that  we  may  rightly  make  concerning  a  prin- 
ciple depend  on  our  definition  of  the  principle.  If  heredity  is  defined  as  absence 
of  the  power  to  vary,  Prof.  Williams's  contention  may  be  justified.  If,  on  the  other 
hand,  we  define  it  as  the  power  to  maintain  a  type  in  the  midst  of  variation,  we 
must  regard  it  as  one  of  the  fundamental  characteristics  of  the  organic  world. 

79 


8o  ANALYSIS  OF    THIJ   FOUR    PRINCIPLES. 

These  six  conditions  all  relate  to  reproduction.  The  first  and 
second  are  that  there  must  be  reproduction,  and  that  it  must  be 
sufficient  with  the  aid  of  adaptation  to  perpetuate  the  race.  The 
third  and  fourth  are  that  the  reproduction  must  result  in  individuals 
more  or  less  departing  from  the  average  character  of  the  parents,  but 
corresponding  with  them  in  their  fundamental  character.  The  fifth 
is  that  reproduction  involves  the  cooperation  of  separate  individuals 
and  binds  the  intergenerating  group  together  in  a  common  heredity. 
The  sixth  is  that  divergence  of  character  depends  on  the  prevention 
of  free  intergeneration,  loosening  the  bond  of  common  descent  be- 
tween the  isolated  sections,  and  so  opening  the  way  for  the  divergent 
forms  that  variation  and  heredity  controlled  by  segregation  are  per- 
mitted to  produce.  The  causes  preventing  free  intergeneration,  and 
opening  the  way  for  divergence,  may  lie  in  the  organism  or  be  imposed 
from  without. 

2    Six  Conditions  on  which  the  Evolution  of  Habitudinal  Types  must  rest. 

First,  the  power  of  influencing  associates;  second,  success  (that 
is,  the  number  of  the  socially  endowed  individuals  must  be  sufficient 
to  keep  up  the  organization) ;  third,  innovation  (that  is,  tentative 
diversity  in  the  action  of  individuals  in  invention  and  initiation  by 
means  of  experiment,  comparison,  and  repetition  of  the  best) ;  fourth, 
tradition  (that  is,  influence  by  means  of  example  and  imitation) ;  fifth, 
free  association  and  communication  within  the  social  group;  sixth, 
segregate  association  setting  limits  to  the  sphere  of  free  association 
and  so  controlling  innovation  and  tradition. 

3.   The  Modes  of  the  Four  Principles. 

In  the  classification  which  I  have  found  most  convenient,  each  of 
the  four  principles  of  segregation  is  presented  under  two  main  forms 
or  modes,  besides  a  third  covering  the  reverse  or  regressive  aspects. 
I  also  recognize  that  the  indiscriminate  action  of  any  one  of  the  four 
principles  may  produce  results  that  should  not  be  overlooked.  The 
indiscriminate  principle  sometimes  producing  racial  intensification  is 
indiscriminate  elimination  of  all  but  a  few,  and  the  indiscriminate 
principle  sometimes  producing  habitudinal  intensification  is  indis- 
criminate failure  of  all  but  a  few.  Under  selection  we  have  first 
the  two  modes,  j,  reflexive  selection,  determined  by  the  direct  influ- 
ence of  members  of  the  species  upon  each  other,  as  in  sexual 
selection  and  social  selection,  and  k,  environal  selection,  deter- 
mined by  the  relations  between  the  environment  and  the  species. 
But  each  of  these  modes  may  be  presented  in  its  regressive  aspects 


THE   MODES  OP  THE  POUR   PRINTCIPLES.  8i 

under  /,  regressive  selection,  due  to  the  survival  of  variations  pre- 
viously excluded ;  and  in  its  indiscriminate  aspects  under  2.  indis- 
criminate elimination.  So  also  election,  and  isolation,  and  partition 
has  each  its  reflexive  mode,  produced  by  the  action  of  the  members 
of  the  species  upon  each  other,  and  its  environal  mode,  determined 
by  the  relations  between  the  environment  and  the  species ;  also  its 
regressive  aspects,  caused  by  the  cessation  or  reversal  of  the  influence 
that  has  been  ruling,  and  its  indiscriminate  aspects.  The  letters  (j, 
k,  I,  z)  here  used  in  designating  the  different  forms  correspond  with 
those  used  in  the  tables  given  in  Chapter  VIII. 

4.  The  Reflexive  Mode  of  Influence. 

The  forms  of  reflexive  selection  have  been  more  fully  worked  out 
than  have  those  of  reflexive  isolation,  or  reflexive  election,  or  reflexive 
partition.  Of  the  forms  of  reflexive  selection,  sexual  selection  is 
the  most  familiar;  for  Darwin  discussed  its  effects  on  the  evolution 
of  the  higher  animals  and  especially  emphasized  its  importance  in 
producing  the  different  races  of  man.  It  may  be  found  that  some 
of  the  effects  which  he  attributed  to  this  principle  are  produced 
in  other  ways;  but  there  can  be  no  doubt  that  in  the  evolution  of 
mankind  it  is  a  factor  of  the  greatest  importance.  With  the  advance 
of  civilization  the  action  of  natural  selection  is  checked ;  but  the  result 
is  not  as  disastrous  as  it  otherwise  would  be  but  for  the  increasing 
stringency  of  sexual,  social,  and  institutional  selection  in  preventing 
the  marriage  of  those  who  are  most  deficient.  Darwin  recognized 
that  the  forms  of  sexual  selection  may  not  only  change  without  any 
change  in  the  environment  surrounding  the  species,  and  without 
securing  any  advantage  for  the  species  in  its  relations  to  the  environ- 
ment, but  that  it  may  even  establish  a  standard  of  selection  that  is 
somewhat  at  variance  with  the  standard  maintained  by  natural  selec- 
tion, and  that  it  may  in  such  cases  be  the  deciding  influence,  causing  the 
species  to  lose  certain  characters  which  are  at  the  time  of  the  change  of 
some  advantage  in  its  relations  to  the  environment.  This  he  thought 
must  have  been  the  case  when  the  ancestors  of  the  human  race  first  lost 
their  covering  of  hair.  (See  Descent  of  Man,  Chap.  XX.)  The  em- 
phasis that  Darwin  laid  on  the  action  of  sexual  selection  in  securing 
the  coordination  between  the  sexual  instincts  of  either  sex  and  the 
instincts  and  palpable  qualities  of  the  other  sex  has  gradually  led  to 
the  recognition  of  certain  other  coordinations  between  members  of 
the  same  race,  which  must  be  secured  by  other  forms  of  reflexive  selec- 
tion. These  other  forms  are  like  sexual  selection,  in  that  they  are 
subject  to  change  without  change  in  the  environment  of  the  species. 


82  ANALYSIS   OF   THE   FOUR   PRINCIPLES. 

II.  Methods  of  the  Reflexive  Mode  of  each  of  the  Four  Principles. 

Producing  demarcation  of  habitudinal         Producing  intensified  divergence  in 
groups:  habits  of  groups: 

Reflexive  partition.  Reflexive  election. 

Conjunctional  partition.  Conjunctional  election. 

Institutional  partition.  Dominational  election. 

Institutional  election. 

Producing  demarcation  of  racial  groups:       Producing  intensified  divergence  in 

racial  characters : 
Reflexive  isolation.  Reflexive  selection. 

Conjunctional  isolation.  Conjunctional  selection. 

Impregnational  isolation.  Dominational  selection. 

Institutional  isolation.  Impregnational  selection. 

Institutional  selection. 
Prudential  selection. 

These  adjectives  designate  the  methods  of  action  by  which  the 
members  of  an  associating  and  intergenerating  group  influence  each 
other  in  such  a  way  that  the  attainment  of  certain  standards  of  train- 
ing and  of  inheritance  are  necessary  to  gain  a  full  share  in  shaping  the 
habits  of  the  group  and  in  propagating  the  species.  But  if  partition 
and  isolation  divide  the  original  group  into  two  or  more  associating 
and  intergenerating  groups,  the  way  is  opened  for  divergence  between 
the  separate  groups ;  for  the  standards  gained  by  reflexive  selection 
and  reflexive  election  are  all  subject  to  gradual  divergence  through  the 
fact  that  different  standards  of  size,  weight,  etc.,  may  bring  survival 
and  success  to  the  separate  groups  in  which  these  differences  are 
found.  For  example,  the  bantam  fowl,  which  for  many  generations 
has  been  isolated  from  the  other  breeds  of  barnyard  fowls,  lays  an  egg 
smaller  than  that  of  the  Shanghai  fowl ;  but  the  coordination  between 
the  average  size  of  the  egg  and  the  average  size  of  the  breed  of 
fowls  laying  the  egg  is  equally  attained  in  each  case  by  filio-parental 
selection,  which  is  one  of  the  forms  of  conjunctional  selection. 

In  our  investigation  of  the  different  methods  of  influence  resulting 
in  segregation,  it  will  greatly  facilitate  our  comprehension  of  the  sub- 
ject if  we  first  consider  how  a  given  method  of  influence  determines 
certain  forms  of  selection ;  then  how  far  the  same  method  of  influence 
shapes  the  forms  of  election  determining  the  acquired  characters  of 
the  group ;  then  what  its  isolating  effects  may  be ;  and  finally  how  the 
same  method  of  influence  may  divide  an  original  group  of  freely  asso- 
ciating individuals  into  several  smaller  groups  and  so  produce  partition. 
Having  mentioned  the  chief  methods  of  the  reflexive  influences  aiding 
in  the  demarcation  and  intensification  of  habitudinal  and  racial 


THE  SEXUAL  FORM   OF   INFLUENCE.  83 

groups,  it  will  next  be  in  place  to  consider  the  way  in  which  each 
method  of  influence  acts  and  the  different  forms  of  action  that  it 
assumes  in  producing  results  under  each  principle. 

1.   The  Forms  0}  the  Conjunctional  Method  oj  each  of  the  Four  Principles. 

Producing  demarcation  of  habitudinal         Producing  intensified  divergence  in 
groups :  habits  of  groups : 

Conjunctional  partition.  Conjunctional  election. 

Family  partition.  Sexual  election. 

Social  partition.  Social  election. 

Filio-parental  election. 

Producing  demarcation  of  racial  groups :       Producing  intensified  divergence  in 

racial  characters : 
Conjunctional  isolation.  Conjunctional  selection. 

Sexual  isolation.  Sexual  selection. 

Social  isolation.  Social  selection. 

Filio-parental  selection. 

The  conjunctional  method  of  influence  is  due  to  the  need  of  coordi- 
nation between  one  sex  and  the  other  in  the  intergenerating  group, 
between  each  member  and  the  others  in  an  associating  group,  and 
between  the  parents  and  offspring  in  each  family  group. 

2.   The  Sexual  Form  oj  Selection,  Election,  and  Isolation. 

Sexual  selection  is  due  to  the  necessity  for  coordination  between  the 
sexual  instincts  and  palpable  qualities  of  the  individual  of  either  sex 
and  the  instincts  and  palpable  qualities  of  the  other  sex,  in  order  to 
secure  propagation  with  survival  in  subsequent  generations.  It  is 
often  assumed  that  in  creatures  lower  than  man  sexual  selection  may 
be  effective  in  establishing  the  normal  standards  of  prowess  and  dis- 
play in  the  male  sex,  but  that  it  avails  very  little  in  determining  the 
standards  of  attainment  in  the  female  sex.  This  is  in  a  considerable 
degree  true  of  species  in  which  the  male  is  the  party  that  seeks  and 
calls  for  a  mate ;  but  even  in  these  species  the  answering  call  of  the 
female  is  often  a  necessary  feature  in  the  attainment  of  suitable  mat- 
ing ;  and  the  hen-bird  that  has  lost  her  voice  goes  desolate.  In  some 
species  of  insects  the  call  for  a  mate  comes  from  the  male,  and  the  part 
of  the  female  is  to  respond  by  leaving  its  distant  hiding-place  and  com- 
ing to  the  male.  The  methods  of  one  such  species  are  described  in 
my  paper  on  Intensive  Segregation,  reproduced  in  Appendix  II  of  this 
volume. 

Sexual  election  is  due  to  the  necessity  for  coordination  between  the 
acquired  habits  and  standards  of  the  individual  of  either  sex  and 
the  sexual  instincts,  as  well  as  the  acquired  habits  arid  standards  of 


84  ANALYSIS  OF  THE    POUR   PRlNCIPIvES. 

the  other  sex,  in  order  that  the  individual  may  secure  success  and 
influence  in  the  community. 

WilHam  E.  D.  Scott,  curator  of  ornithology  of  Princeton  University, 
tells  of  a  red-winged  blackbird  which,  for  the  sake  of  testing  the  power 
of  tradition,  was,  from  the  day  he  left  the  egg,  "  brought  up  by  hand,  in 
a  room  by  himself,  away  from  all  sounds,  as  was  supposed.  The  result 
was  that  when  the  time  came  for  him  to  sing  he  crowed  like  a  rooster. 
It  then  developed  that  every  morning  a  bantam  rooster  had  crowed 
under  his  window."*  Whether  he  was  able  to  win  any  mate  among 
his  fellow  captives  is  not  mentioned ;  but  if  he  had  been  turned  loose 
to  seek  a  mate  among  his  kindred  of  the  wild,  his  inability  to  use  the 
song  of  his  kind  would  certainly  have  given  great  advantage  to  his 
rivals  who  had  learned  the  true  song  of  the  species. 

Sexual  isolation  arises  between  groups  of  the  same  species  that  have 
been  separated  by  geographical  barriers  for  several  generations,  and 
have  in  the  meantime  attained  divergent  forms  of  inherited  characters 
by  which  they  recognize  each  other,  and  different  methods  of  calling 
each  other  and  winning  each  other.  Though  physiologically  any 
cross  between  the  two  races  is  both  fertile  and  vigorous,  psychologi- 
cally they  are  prevented  from  crossing  through  incompatibility  in 
sexual  instincts  and  inherited  endowments. 

I  judge  that  there  is  no  need  of  distinguishing  sexual  partition  from 
sexual  isolation,  for  an  associating  group  determined  by  sexual  habits 
and  instincts  would  surely  be  an  intergenerating  group. 

3.   The  Social  Form  of  Selection,  Election,  Isolation,  and  Partition. 

Social  selection  is  due  to  the  necessity  for  coordination  between  the 
social  instincts  and  endowments  of  the  individual  and  the  social 
instincts  and  endowments  of  the  race,  in  order  that  the  individual 
should  secure  a  chance  to  survive  and  propagate.  We  find  that  under 
the  same  environment  there  are  many  possible  instinctive  calls,  and 
many  arrangements  of  color,  and  many  combinations  of  inherited 
odors,  by  which  the  individuals  of  one  race  recognize  each  other.  By 
means  of  characters  that  we  are  unable  to  note  the  bees  of  one  hive 
recognize  each  other,  and  there  is  reason  to  believe  that  serious 
deficiency  in  any  essential  character  would  lead  to  the  exclusion  of 
the  deficient  individual  from  the  privileges  of  the  community.  The 
power  to  recognize  one's  own  race  by  scent  is  not  as  wonderful  as  the 
power  of  the  bloodhound  to  distinguish  between  individuals  in  the 
same  way.     Not  only  must  the  distinctive  character  of  the  race  be 


*  See  The  Outlook  (of  New  York)  for  July  5,  1902. 


THE   SOCIAL  FORM  OF   INFIvUENCE.  85 

found  in  the  individual,  but  the  individual  must  be  able  to  recognize 
those  of  his  own  clan,  and  to  keep  with  them  in  time  of  rapid  flight.  A 
near-sighted  deer  or  cotton-tail  rabbit  would  be  in  danger  of  losing  his 
life  through  losing  the  trail  which  the  leaders  have  taken,  raising  their 
tails  high  that  they  may  be  seen  by  those  which  follow. 

Social  election  is  a  similar  principle  resting  on  acquired  habits  and 
characters.  It  is  due  to  the  necessity  for  coordination  between  the 
social  habits  of  the  individual  and  the  social  standards  of  the  com- 
munity, in  order  to  secure  success  and  influence.  The  knowledge  of 
a  common  language  is  recognized  as  a  fundamental  need  of  a  human 
community,  and  there  is  a  similar  need  in  any  community  of  animals. 
With  the  lower  creatures  this  need  is  largely  met  by  inherited  instincts, 
which  determine  the  calls  and  warning  cries  and  the  interpretations 
that  they  receive;  but  in  some  cases  the  training  obtained  by  the 
young  from  the  example  of  their  elders  is  an  important  element  in  the 
transmission  of  the  language.  In  such  cases  the  standard  is  main- 
tained by  social  election. 

It  is  easy  to  understand  that  the  red- winged  blackbird  mentioned 
above,  which  learned  to  crow,  but  had  no  chance  to  learn  the  normal 
song  of  the  species,  would  not  have  much  influence  on  the  musical 
attainments  of  the  next  generation  of  the  species;  and  perhaps  his 
failure  in  this  respect  would  lessen  his  influence  as  a  leader  in  other 
things. 

One  reason  for  believing  that  example  has  no  small  influence  in 
shaping  the  songs  of  certain  species  of  birds,  is  found  in  the  fact  that 
Japanese,  who  highly  appreciate  the  song  of  the  uguisu  (sometimes 
called  an  oriole),  are  very  careful  that  the  young  birds  that  are  taken 
from  the  nests  of  wild  birds  in  the  woods  and  brought  up  by  hand 
shall  have  opportunity  to  hear  only  the  most  accomplished  adult 
singers  during  their  period  of  growth. 

Social  isolation. — When  two  groups  of  a  species  have  been  separated 
by  geographical  barriers  for  many  generations,  they  are  liable  to  gain 
divergent  social  habits  and  instincts,  and  different  calls,  rendering 
them  unfit  for  being  associated  in  the  same  intergenerating  group 
when  brought  into  the  same  district.  The  geographical  isolation  has 
ceased,  but  they  continue  as  separate  intergenerating  groups  through 
the  influence  of  social  isolation. 

Social  partition. — In  so  far  as  the  social  incompatibilities  holding 
two  groups  apart  are  due  to  acquired  habits  and  tend  to  produce  sepa- 
rately associating  habitudinal  groups,  the  process  may  be  called 
social  partition. 


86  ANALYSIS  OF  THE   FOUR  PRINCIPLES. 

4.   The  Filio-parenial  Form  of  Selection  and  Election,  and  Family 
Partition. 

Filio-parental  selection  is  due  to  the  dependence  of  survival  on  the 
coordination  between  the  inherited  needs,  powers,  and  instincts  of  the 
young  by  which  they  are  related  to  their  parents  and  the  inherited 
adaptations,  powers,  and  instincts  of  the  parents  by  which  they  are 
related  to  the  young.  In  my  paper  on  Intensive  Segregation  I  referred 
to  the  necessity  for  coordination  between  the  size  of  the  child's  head 
and  the  size  of  the  pelvis  in  the  mother. 

In  Science  for  December  24,  1897,  page  942,  G.  A.  Reid,  of  Southsea, 
England,  calls  attention  to  the  increasing  difficulty  of  childbirth  in 
civilized  women,  resulting  from  the  regressive  selection  occasioned  by 
the  skillful  appliances  of  modern  science.  He  says:  "Indeed  the 
recent  advance  of  obstetric  science  has  enabled  so  many  of  the  other- 
wise unfit  to  survive  among  us  for  some  generations  past  that  now 
numerous  women  are  quite  incapable  of  parturition  without  instru- 
mental aid."  In  a  note  he  adds:  "It  is  not  possible  that  the  saving 
of  so  many  narrow-hipped  women  and  big-headed  children  can  have 
left  the  race  unaffected." 

Filio-parental  election  is  due  to  the  necessity  for  coordination  be- 
tween the  acquired  habits  of  the  young  and  the  habits,  instincts,  and 
endowments  of  the  parents  in  order  to  gain  success  and  influence. 

The  term  "  family  isolation  "  may  be  needed  in  describing  the 
usual  relationship  of  mates  in  certain  species ;  but  with  mammals  it 
has  been  found  that  in-and-in  breeding,  continued  through  many 
generations,  tends  to  degeneration,  and,  therefore,  to  extinction. 

Family  partition  arises  in  so  far  as  the  separation  of  families  leads 
to  the  formation  of  separate  habits  and  acquired  characters.  It  is 
doubtful  whether  the  term  "filio-parental  partition"  is  needed,  as 
the  term  "  family  partition  "  seems  to  be  more  appropriate. 

5.   The  Forms  of  the  Dominational  Method  of  Influence. 

■    Producing  intensified  divergence  in  the  habits  of  groups : 
Dominational  election. 
Producing  intensification  of  racial  groups: 
Dominational  selection. 

Sustentational  domination. 
Protectional  domination. 
Nidificational  domination. 
Mating  domination. 
Prepotential  domination. 

The  dominational  method  of  influence  does  not  depend  on  superior 
adjustments  to  the  environment,  but  is  due  to  the  power  to  outdo, 


DOMINATIONAL  AND  IMPREGNATIONAIv  INFLUENCES.  87 

overcome,  and  forestall  rivals  of  the  same  species  in  taking  possession 
of  mates  or  of  resources  and  in  seizing  on  opportunities.  The  import- 
ance of  conflict  and  rivalry  between  individuals  of  the  same  group  in 
gaining  possession  of  resources  and  mates  was  discussed  in  my  paper 
on  Intensive  Segregation  under  the  term  that  I  now  use.  It  has  since 
then  been  discussed  by  Karl  Pearson  in  his  "Grammar  of  Science," 
under  the  term  "inter-group  selection."  The  chief  objection  to  his 
term  is  that  it  ought  naturally  to  include  all  the  forms  of  what  I  have 
called  "reflexive  selection;"  but  this  is  not  in  accordance  with  the 
definitions  he  has  given. 

Dominational  selection  is  due  to  inherited  powers  for  overcoming 
rivals  giving  a  larger  share  in  propagation  and  survival  through  con- 
trol of  resources  and  mates. 

Dominational  election  is  due  to  acquired  powers  for  overcoming 
rivals  giving  superior  success  and  influence  in  the  associating  group. 
As  prepotence  is  determined  entirely  by  inherited  powers,  domina- 
tional election  can  have  no  influence  on  prepotence.  Severe 
competition  with  domination  is  a  condition  that  gives  importance 
to  isolation  and  partition,  but  these  principles  are  not  introduced 
without  other  causes,  such  as  migration  or  transportation. 

6.  The  Forms  0}  the  Impregnational  Method  of  Influence. 
Producing  demarcation  of  racial  Producing  intensification  of  racial 

groups:  groups: 

Impregnational  isolation.  Impregnational  selection. 

Dimensional  isolation.  Dimensional  interselection. 

Structural  isolation.  Structural  interselection. 

Potential  isolation.     '  Potential  selection. 

Segregate  fecundity.  Fecundal  selection. 

Segregate  vigor. 
Segregate  adaptation. 
Segregate  freedom  from  competition. 
Segregate  escape  from  enemies. 

The  impregnational  method  of  influence  is  due  to  the  need  of  coor- 
dination between  the  size,  structure,  sexual  elements,  and  functions 
of  each  sex  and  the  related  characters  of  the  other  sex,  in  any  inter- 
generating  group,  in  order  to  secure  a  sufficient  number  of  impreg- 
nated germs  with  the  least  expenditure  and  waste.  Inasmuch  as 
the  influences  shaping  impregnation  are  inherited  and  not  acquired, 
their  chief  effects  are  on  racial  rather  than  habitudinal  groups.  We 
therefore  have  no  occasion  to  consider  impregnational  partition  and 
election. 

Of  the  forms  of  impregnational  isolation,  the  first  five  as  given  above 
were  so  fully  considered  in  my  paper  on  Divergent  Evolution*  that  it 


*  See  Appendix  I,  where  part  of  the  paper  is  reproduced. 


88  ANALYSIS  OP  THE   FOUR   PRINCIPIvES. 

will  not  be  necessary  to  give  much  space  to  them  here.  Of  the  forms 
of  impregnational  selection,  the  last  of  the  four  mentioned  above  was 
presented  in  my  paper  on  Intensive  Segregation*  as  a  factor  of  pro- 
found influence  in  the  intensification  of  racial  groups.  The  term  there 
used  is  "  fecundal  intension  "  which  indicated  the  result  of  the  process 
which  I  call  "fecundal  selection." 

7.   The  Dimensional  Form  of  Impregnational  Selection,  and  0}  Isolation. 

The  dimensional  form  of  impregnational  selection  is  due  to  the  neces- 
sity for  the  coordination  of  the  sexes  of  the  intergenerating  group,  in 
such  a  way  that  incompatibility  of  size  shall  not  interfere  with  im- 
pregnation. Compatibility  in  this  respect  is  maintained  within  the 
intergenerating  group ;  for  if  any  individual  is  so  far  above  or  below 
the  average  size  as  to  render  mating  difficult,  the  chances  are  that  the 
descendants  of  that  individual  will  be  comparatively  few,  or  perhaps 
entirely  wanting.     This  may  be  called  dimensional  interselection. 

Dimensional  isolation  arises  when  local  varieties  of  birds  and  mam- 
mals, that  have  become  very  divergent  in  size,  are  brought  to  the 
same  district.  An  example  is  seen  in  bantams  and  Shanghai  fowls. 
There  are  also  certain  breeds  of  horses  and  of  asses  that  are  completelv 
prevented  from  crossing  with  certain  other  breeds  of  the  same  species, 
through  incompatibility  in  size.  Dimensional  and  structural  isola- 
tion are  terms  that  convey  a  fairly  definite  meaning,  as  it  is  evident 
that  the  isolation  must  be  brought  about  by  the  relations  of  members 
of  the  same  species  to  each  other,  and  not  through  their  relations  to 
the  environment  surrounding  the  species.  There  would,  however,  be 
indefiniteness  in  the  terms  "  dimensional  "  and  "structural  "  selection ; 
for  size  and  structure  have  survival  value  in  the  relations  of  the 
members  of  the  species  to  the  environment,  as  well  as  in  their  relations 
to  each  other.  I  therefore  prefer  to  call  the  former  of  these  factors 
the  dimensional  form  of  impregnational  selection  and  the  latter  the 
structural  form  of  impregnational  selection.  If  briefer  terms  are 
desired,  it  will  perhaps  be  allowable  to  use  the  forms  "dimensional 
interselection"  and  "  structural  interselection." 

8.   The  Structural  Form  of  Impregnational  Selection,  and  Isolation. 

Structural  interselection. — The  males  of  many  species,  especially 
among  insects,  are  furnished  with  clasping  organs  for  holding  the 
females  during  mating,  and  in  some  cases  both  sexes  are  thus  equipped. 
The  structural  form  of  impregnational  selection  maintains  the  average 
characters  that  are  necessary  for  the  coordination  of  these  and  all 
other  sexual  organs  and  of  all  organs  that  are  necessary  for  the  suc- 

*  See  Appendix  II. 


STRUCTURAL  AND  POTENTIAIv  SEGREGATION.  89 

cessive  steps  by  which  impregnation  is  reached.  This  last  clause  is 
added,  for  we  observe  that  in  the  language  of  recent  botanists  the 
stamens  and  pistils  of  plants  are  not  sexual  organs;  and  "pollen 
grains  are  asexual  spores."*  This,  however,  does  not  change  the  fact 
that  in  order  to  secure  fertilization  the  pollen  grain,  after  reaching  the 
stigma,  must  be  able  to  send  out  a  pollen  tube  long  enough  and  pene- 
trating enough  to  descend  through  the  length  of  the  pistil  to  the  center 
of  the  ovule,  through  the  nucellus  and  embryo-sac.  The  coordinations 
required  for  securing  these  and  many  other  steps  in  the  process  of 
fecundation  are  maintained  by  impregnational  selection,  and  so  far 
as  they  depend  on  the  form  and  structure  of  organs  we  may  call  the 
process  "structural  interselection."  The  propagation  of  every  sex- 
ually reproducing  plant  and  animal  must  depend  on  such  coordi- 
nations. 

Structural  isolation  arises  when  local  varieties  that  have  become  so 
far  divergent  in  structure  as  to  be  incompatible  are  brought  together 
in  the  same  district.  Darwin  suggested  that  difference  in  the  length 
of  the  pollen  tubes  and  the  pistils  may  be  the  cause  preventing  crosses 
between  certain  species  of  plants. 

9.   The  Potential  Form  of  Selection  and  Isolation. 

Potential  selection. — There  are  characters  more  fundamental  than 
form  and  structure  that  must  be  coordinated  in  order  to  secure  the 
fertilization  of  the  ova  that  produce  the  next  generation.  The  pollen 
of  one  species  of  plants  is  usually  either  partially  or  entirely  ineffective 
if  it  falls  upon  the  stigma  of  another  species,  even  though  both  species 
are  of  the  same  genus.  There  are  also  certain  species  having  two 
kinds  of  stamens  producing  two  kinds  of  pollen ;  and  the  pollen  from 
the  short  stamens  is  said  to  be  most  effective  upon  the  stigmas  of  the 
short  styles,  and  the  pollen  from  the  long  stamens  most  effective  upon 
the  stigmas  of  the  long  styles.  As  each  flower  produces  either  a  long 
style  and  short  stamens  or  a  short  style  and  long  stamens,  the  dis- 
criminate prepotence  just  described  insures  cross-fertilization. f  But 
our  present  interest  is  in  the  fact  that  in  pollen  grains  there  are  char- 
acters of  an  obscure  nature  which  are  of  great  importance  in  insuring 
the  required  potency.  There  is  reason  to  believe  that  in  every  species 
depending  on  sexual  reproduction  there  must  be  more  or  less  potential 
selection,  by  which  the  coordination  of  the  sexual  elements  enabling 
them  to  coalesce  is  maintained. 

Potential  isolation  occurs  in  the  two  forms,  prepotential  isolation 
and  complete  potential  isolation.     Complete  potential  isolation  exists 

*  See  Plant  Structures,  by  John  M.  Coulter;  Appleton  &  Co.,  1900;  pp.  176, 177. 
t  See  Plant  Relations,  by  John  M.  Coulter,  pp.  129,  130. 


90  ANALYSIS  OF   THE   FOUR   PRINCIPLES. 

between  types  when  their  sexual  elements  are  incapable  of  uniting  in 
fertilized  germs  under  any  conditions.  Prepotential  isolation  exists 
when  cross-fertilization  is  possible  if  the  alien  fertilizing  element  has 
the  advantage  of  being  applied  some  time  in  advance ;  but  if  the  fer- 
tilizing element  of  the  same  variety  or  species  is  applied  at  the  same 
time,  or  in  some  cases  at  any  time  during  several  hours  that  follow, 
mixed  fertilization  is  prevented  by  the  prepotence  of  the  pure  fertiliz- 
ing element. 

10.   Fecundal  Selection. 

Fecundal  selection  secures  coordination  between  the  number  of  ova 
and  the  supply  of  fertilizing  elements  required  for  the  fertilizing  of  the 
same  in  connection  with  methods  used  to  secure  the  bringing  of  these 
elements  to  the  ova.  The  coordination  between  the  number  of  fer- 
tilized ova  and  the  power  of  the  parents  or  community  for  production, 
rearing,  and  training  of  offspring  is  secured  by  what  I  call  filio-parental 
selection.  The  combined  action  of  these  two  principles  tends  to 
bring  the  standard  of  fertility  for  the  group  up  to  the  highest  point 
that  is  permitted  by  the  average  capacity  of  the  parents  for  producing, 
rearing,  and  training  the  ofiFspring.  In  my  paper  on  Divergent  Evolu- 
tion, read  before  the  Linnean  Society  in  1887,  after  referring  to  the 
principles  of  segregate  fecundity  and  segregate  vigor,  I  made  the  fol- 
lowing statement  concerning  "The  Nature  of  Cumulative  Fertility" : 

*  *  *  Fertility  increases  through  the  breeding  together  of  the  more  fertile 
resulting  from  the  fact  that  more  than  half  of  each  generation  are  the  offspring  of 
parents  of  more  than  average  fertility.  As  the  breeding  together  of  the  more  vig- 
orous and  the  better  adapted,  caused  by  their  superior  success,  tends  to  increase 
the  vigor  and  adaptation  of  successive  generations,  *  *  *  so  the  breeding 
together  of  the  more  fertile,  caused  by  the  larger  proportion  of  offspring  produced 
by  the  more  fertile,  tends  to  increase  the  fertility  of  successive  generations.  Among 
those  that  would  be  equally  productive  if  equally  nourished,  the  ratio  of  propaga- 
tion varies  directly  as  the  degree  of  sustentation  above  a  certain  minimum  (and 
perhaps  below  a  certain  maximum),  and,  therefore,  directly  as  the  degree  of 
adaptation  that  secures  this  sustentation.  This  propagation  according  to  degrees  of 
adaptation  to  the  environment  is  what  I  understand  by  natural  selection.  But  among 
those  that  are  equally  adapted  to  the  environment  the  ratio  of  propagation  varies 
directly  as  the  ratio  of  fertility.  This  propagation  according  to  degrees  of  fertility 
is  what  I  call  the  law  of  cumulative  fertility.  (See  Jour.  Linnean  Society,  Zoology, 
vol.  XX,  pp.  247,  248.) 

In  my  paper  on  Intensive  Segregation,  published  in  1889, 1  discussed 
this  principle  under  the  term  "  fecundal  intension,"  which  I  still  retain 
to  designate  the  influence  of  the  principle  in  transforming  races  and 
species,  which  was  the  point  of  view  chiefly  considered  in  that  paper. 
I  there  called  attention  to  the  fact  that  if  in  an  isolated  portion  of  a 
species  the  type  of  variation  that  attains  the  highest  fertility  is  not 


FECUND AL  SELECTION.  9 1 

the  same  as  in  the  body  of  the  original  species,  the  average  form  of  the 
isolated  group  will  in  a  few  generations  become  different  from  the 
average  form  in  the  original  stock,  even  though  the  environment  sur- 
rounding each  is  the  same.  I  also  noted  that  "the  chief  check  to  this 
law  of  cumulative  fertility  is  found  in  the  antagonistic  (that  is,  rival, 
and  sometimes  severely  competing)  law  of  cumulative  adaptation 
through  adaptational  selection."  [See  Appendix  II,  sec.  I,  8,  (15).] 
I  also  referred  to  the  cooperation  of  the  two  factors  in  the  fol- 
lowing words: 

The  combined  action  of  these  two  laws  results  in  the  triumphant  development 
of  the  most  fertile  of  the  best  fitted  or  the  best  fitted  of  the  most  fertile.  Another 
result  from  their  combined  action  is  that  in  species  well  adjusted  to  the  environ- 
ment the  typical,  that  is,  the  average,  form  of  the  species  is  not  only  the  best 
adapted,  but  it  is  the  most  fertile;  and  this  correlation  between  fertiHty  and  adap- 
tation in  the  average  form  of  the  species  or  race  is  a  strongly  conservative  principle, 
tending  to  prevent  the  over-rapid  transformation  of  the  race  or  species. 

In  the  more  exact  definition  of  fecundal  selection  given  above  I 
point  out  that  the  chief  condition  restraining  the  action  of  this  prin- 
ciple is  found  in  the  average  power  of  parents  for  parental  nourishing 
and  postnatal  rearing  and  training  of  offspring.  The  initial  fertility 
depends  on  the  abundance  of  the  ova  and  the  proportionate  correla- 
tion between  the  numbers  of  the  ova  and  the  fertilizing  cells;  while 
the  final  fertility  must  depend,  not  only  on  these  correlations  produc- 
ing initial  fertility,  but  on  that  form  of  filio-parental  selection  which 
secures  the  correlation  between  initial  fertility  and  the  power  of  the 
parents  to  nourish  and  develop  the  ova  after  fertilization  and  to  rear 
and  train  the  young  till  they  are  capable  of  independent  life.  If  the 
degree  of  initial  fertility  overtaxes  the  power  for  producing  or  rearing 
offspring,  the  final  fertility  may  fall  far  below  the  need  for  survival, 
while  if  the  young  could  only  reach  maturity  in  good  condition  the 
fertility  would  be  far  above  the  need. 

Certain  domestic  breeds  show  clearly  the  nature  of  the  disaster  that 
would  come  to  any  species  under  natural  conditions  if  filio-parental 
selection  were  so  far  suspended  as  to  break  down  the  coordination 
between  the  initial  fertility  and  the  power  of  the  parents  to  bring  the 
young  to  maturity.  The  Leghorn  hen  lays  from  1 50  to  200  eggs  in  a 
year,  and  seldom  cares  to  set.  It  is  evident  that  such  a  race  would 
run  great  risk  of  extinction  if  separated  from  the  care  of  those  who  are 
in  the  habit  of  providing  methods  for  the  hatching  and  rearing  of  the 
young.  Even  if  some  of  the  race  should  regain  the  instincts  required 
for  hatching  out  and  rearing  their  young,  how  impossible  would  be  the 
task  of  hatching  and  raising  twelve  or  thirteen  full  broods  in  a  year. 


92  ANALYSIS   OF  THE)  FOUR  PRINCIPLES. 

Having  suspended  laying  eggs  for  a  few  days,  the  hen  might  devote 
herself  faithfully  to  setting  on  a  nest  full  of  eggs  needing  warmth  for 
hatching;  but  before  the  chicks  were  ready  to  appear,  the  necessity 
would  return  for  giving  herself  to  laying  eggs.  In  a  state  of  nature 
such  an  unbalanced  development  of  the  powers  that  should  cooperate 
in  the  process  of  reproduction  could  never  have  become  so  marked ; 
for  the  one-sided  development  of  any  individual  causing  it  to  pro- 
duce even  a  few  eggs  or  young  in  excess  of  the  normal  number  would 
in  some  degree  impair  its  power  of  leaving  successful  offspring.  The 
failure  of  such  individuals  to  leave  their  full  proportion  of  offspring, 
and  the  effect  of  this  failure  on  the  race,  I  describe  as  the  action 
of  filio-parental  selection  setting  limits  to  the  range  within  which 
fecundal  selection  may  act. 

1 1 .  Fecundal  Selection  in  Human  Races. 

One  of  the  most  striking  examples  of  the  loss  of  fertility,  and  of  the 
gradual  extinction  that  follows,  is  found  in  the  experience  of  the  Poly- 
nesians since  their  contact  with  Europeans.  In  but  few  of  the  islands 
of  the  Pacific  have  the  aborigines  been  displaced  by  conflict  of  arms 
or  by  industrial  competition.  The  great  cause  of  their  disappear- 
ance, during  the  earlier  periods  of  intercourse  was  their  inability  to 
cope  with  the  microbes  of  measles,  smallpox,  leprosy,  and  other  dis- 
eases, unknown  to  them  before  the  arrival  of  Europeans  and  Chinese. 
But  in  many  groups  of  these  islands,  and  especially  in  Hawaii,  that 
stage  of  disadvantage  is  now  largely  past,  through  the  protection 
gained  from  Western  science.  Still  the  steady  decrease  in  numbers 
continues,  for  the  birth  rate  is  not  sufficient  to  meet  the  natural  rate 
of  mortality.  And  there  is  no  reason  to  attribute  this  small  birth 
rate  to  poverty  or  to  prudential  selection.  Whatever  the  antecedent 
causes  may  have  been,  the  present  condition  is  failure  to  meet  the 
demands  of  fecundal  selection. 

The  nature  of  the  deficiency  is  more  fully  realized  when  the  decrease 
of  the  Polynesian  race  in  their  original  home  is  compared  with  the 
increase  of  the  African  race  in  North  and  South  America. 

12.  Statistical  Methods  in  the  Study  of  Fertility. 
Karl  Pearson  has  within  a  few  years  published  several  interesting 
discussions  on  the  subject  of  fertility  as  a  factor  in  the  evolution  of 
civilized  man,*  in  which  he  has  reached  by  statistical  methods  some 


*  See  "Chances  of  Death  and  Other  Studies  in  Evolution,"  Chapter  III,  entitled 
"Reproductive  Selection,"  published  by  Edward  Arnold,  London  and  New  York, 
1897;  also  "The  Grammar  of  Science,"  second  edition,  published  by  A.  C.  Black, 
London,  1900;  in  the  sections  devoted  to  reproductive  or  genetic  selection. 


PECUNDAL  SELECTION   IN   HUMAN   RACES.  93 

of  these  results  which  I  had  previously  reached  by  other  methods. 
The  points  in  which  our  results  most  fully  correspond  are  that  fertility 
tends  to  increase  till  checked  by  some  other  form  of  selection ;  that 
transformation  of  race  may  be  produced  by  this  principle ;  and  that, 
in  a  species  well  adjusted  to  the  environment,  the  typical  form  of  the 
species  is  not  only  the  best  adapted,  but  it  is  the  most  fertile.  Con- 
cerning "a  tendency  to  increasing  fertility  in  man,"  he  says:  "We 
can  not  doubt  that  reproductive  selection  would  steadily  tend  to  alter 
the  mean  fertility  in  man,  unless  it  were  somehow  held  stringently  in 
check.  It  is  a  point  which  seems  to  me  of  the  utmost  significance 
that  (as  revealed  by  the  statistics  of  4,390  Anglo-Saxon  families) 
allowing  for  the  proportion  of  the  unmarried  in  the  population,  about 
one-fifth  to  one-sixth  only  of  the  adults  produce  quite  one-half  of  the 
next  generation,  and  any  correlation  between  inheritable  (physical 
or  social)  characteristics  and  fertility  must  thus  sensibly  influence 
that  next  generation. "  (The  Chances  of  Death,  pp.  82,  83.)  In  regard 
to  the  transforming  influence  of  this  principle  he  says :  "I  think  there 
is  quantitative  evidence  that  types  of  life  may  change  without  the 
action  of  organic  or  inorganic  environment,  i.  e.,  solely  owing  to  some- 
thing inherent  in  their  constitution.  One  such  factor  of  evolution, 
genetic  selection,  I  shall  refer  to  later."  (The  Grammar  of  Science, 
p.  376.)  Of  the  relation  of  fertility  to  type  he  says:  "For  stable 
races  there  is  a  strong  tendency  for  the  character  of  maximum  fer- 
tility to  become  one  with  the  character  which  is  the  type."  (The 
Grammar  of  Science,  p.  444.) 

The  importance  of  applying  statistical  methods  of  investigation  to 
the  problems  of  human  evolution  can  not  be  overstated ;  but,  for  the 
full  success  of  these  methods,  it  is  necessary  that  the  nature  of  the 
factors  in  their  fundamental  relations  to  each  other  should  be  clearly 
apprehended  and  clearly  stated  in  the  definitions  of  the  terms  by 
which  the  different  influences  are  designated.  This  necessity  seems 
to  require  that  we  should  have  some  knowledge  of  the  probable  factors 
before  we  can  even  collect  the  statistics  that  will  be  of  avail  in  giving 
a  quantitative  measurement  of  the  effects  of  any  one  factor.  We 
must  have  a  clear  conception  both  of  the  scope  and  of  the  limits  of  a 
given  factor  or  we  may  ascribe  to  it  effects  that  are  produced  by  other 
factors,  or  ascribe  to  other  factors  effects  produced  by  it.  By  way  of 
illustration,  we  may  ask  what  is  the  scope  and  what  are  the  limits  of 
the  terms  fertility  and  reproductive  selection  as  used  by  Karl  Pearson  ? 
When  he  says  (The  Chances  of  Death,  p.  81),  "Hence  it  would  seem 
that  any  characteristic  or  organ — such,  for  instance,  as  stature  or  size 
of  pelvis  in  the  mother — correlated  with  fertility  would  be  progres- 


94  ANALYSIS  OF  THE   FOUR  PRINCIPLES. 

sively  changed,  *  *  *  owing  to  reproductive  selection,"  we  are 
led  to  suppose  that  reproductive  selection  depends  in  part  on  that 
fertility  which  depends  on  the  fitness  of  the  pelvis  of  the  mothers  for 
fulfilling  the  functions  of  pregnancy  and  parturition.  We  also  reflect 
that  in  all  mammahan  mothers  there  are  organs  on  the  fitness  of 
which  for  furnishing  nourishment  to  the  young  must  depend  the  suc- 
cess of  the  process  of  reproduction.  Does  this  form  of  survival  of  the 
fittest  (or  failure  of  the  least  fitted  to  leave  mature  offspring)  come 
under  the  principle  of  reproductive  selection  as  defined  by  our  author? 
Again,  we  know  that,  in  the  case  of  many  species,  the  males  who  are 
best  fitted  for  driving  off  rivals,  or  who  are  best  fitted  for  attracting 
the  females,  leave  the  most  offspring.  Is  their  success  in  reproducing 
an  example  of  reproductive  selection  ?  According  to  Darwin's  nomen- 
clature this  process  is  called  sexual  selection;  but  Karl  Pearson's 
definition  of  sexual  selection  is :  "  All  differential  mating  due  to  taste, 
habit,  or  circumstance,  which  prevents  a  form  of  life  from  freely  inter- 
crossing. If  this  goes  on  for  a  sufficient  period  during  which  differen- 
tiation of  type  is  in  progress,  the  principle  of  correlation  may  account 
for  a  sufficient  differentiation  in  reproductive  organs  or  functions 
to  render  intercrossing  physiologically  or  mechanically  difficult,  dis- 
tasteful, or  even  impossible,  and  accordingly  give  rise  to  the  relative 
or  absolute  sterility  of  the  differentiated  types,  i.  e.,  to  the  origin  of 
species."  (Grammar  of  Science,  p.  418.)  It  is  very  pleasant  to  find 
such  full  recognition  of  the  principle  of  isolation,  even  though  it  be 
under  another  name ;  but  the  question  at  present  is,  where  does  he  place 
the  survival  through  successful  propagation  of  those  who  are  best  able 
to  win  partners?  Does  he  classify  it  as  a  form  of  natural  selection,  or 
as  a  form  of  sexual  selection,  which  has  been  so  defined  as  to  be  equiv- 
alent to  isolation;  or  is  it  included  under  reproductive  selection? 
After  reading  the  passage  already  quoted  from  page  81  of  The  Chances 
of  Death,  the  l^st  of  these  three  suppositions  seems  the  most  probable ; 
and  still  more  so  after  reading  the  following  definition  of  reproductive 
selection  given  on  pages  65  and  66 : 

If  there  be  any  sensible  correlation  between  fertility  and  the  size  of  any  organ  or 
intensity  of  any  characteristic  in  male  or  female — that  is,  if  deviations  in  excess 
(or  defect)  from  the  mean  of  this  organ  correspond  to  a  greater  fertility  than  devi- 
ations in  defect  (or  excess) — then  under  the  action  of  heredity  we  have  a  vera 
causa  of  progressive  evolution  in  this  organ;  for  an  increasing  number  of  individ- 
uals will  be  born  with  the  organ  in  excess  (or  defect),  and  consequently  the  mean, 
and  most  probably  the  variation  about  the  mean,  of  the  general  population  will  be 
progressively  modified.  The  result  is  somewhat  similar  to  that  due  to  artificial 
selection  in  the  case  of  domestic  animals,  where  without  extermination  greater 
fertility  is  given  to  selected  parents  by  pairing  them  only,  or  by  pairing  them  more 


THE   IMPORTANCE   OF  IMPREGNATIONAL  ISOLATION.  95 

frequently  than  others.  In  a  memoir  on  Regression,  Heredity,  and  Panmixia, 
recently  jjublished,  I  have  ventured  to  term  this  possible  factor  of  progressive 
evolution  "reproductive  selection." 

This  definition  .seems  very  definitely  to  include  not  only  sexual 
selection  but  the  forms  of  reflexive  selection  which  I  have  called  social, 
filio-parental,  dominational,  and  impregnational  selection.  But  we 
can  have  but  little  confidence  that  we  have  reached  the  correct  inter- 
pretation of  the  meaning  he  would  have  us  give  to  the  terms  "  repro- 
ductive selection"  and  "fertility,"  for  when  we  come  to  the  con- 
cluding sentence  of  the  chapter,  on  page  102,  we  read:  "In  civilized 
man  the  survival  of  the  fittest  appears  to  be  replaced  by  the  survival 
of  the  most  fertile,"  which  seems  to  imply  that  fertility  as  he  uses 
it  does  not  depend  on  fitness. 

13.   The  Importance  of  Impregnational  Isolation. 

The  prevention  of  crossing  between  groups  produced  by  the  dif- 
ferent forms  of  impregnational  isolation  is  connected  with  several 
problems  of  great  interest.  After  referring  to  the  terms  segregate 
survival,  segregate  union,  and  "physiological  isolation,"  under  which 
some  of  these  principles  have  been  grouped,  we  will  consider  certain 
of  these  problems. 

( I )  Segregate  survival  has  presented  itself  to  my  mind  in  five  aspects, 
namely :  Segregate  fecundity,  vigor,  adaptation,  freedom  from  competi- 
tion, and  escape  from  enemies. 

These  are  the  influences  that  give  emphasis  to  the  importance  of 
any  form  of  positive  segregation  by  which  those  of  any  one  kind  are 
brought  together  and  enabled  to  breed  together.  It  may  at  first  seem 
that  these  are  simply  the  forms  of  selection  that  are  producing  trans- 
formation within  the  difi"erent  intergenerating  groups.  It  is,  how- 
ever, quite  otherwise;  for  diversity  of  selection  may  exist  in  full 
force  in  two  adjoining  districts,  and  partial  positive  segregation  may 
exist  between  the  two  group*;  of  a  species  occupying  these  districts; 
but,  if  the  mixed  unions  are  as  fertile  as  the  pure  unions,  and  produce 
young  as  successful  in  surviving  as  those  produced  by  the  pure  unions, 
the  probability  is  that  the  two  groups  will  not  become  increasingly 
divergent. 

Impregnational  isolation  has  now  been  presented  under  eight  forms, 
of  which  the  first  three  rest  on  morphological  and  physiological  incom- 
patibilities preventing  or  interfering  with  mixed  unions,  which  ma}'^, 
therefore,  be  called  segregate  union.  The  second  group  of  five  forms 
rests  on  incompatibilities  preventing  either  the  normal  fruitfulness  of 
mixed  unions  or  the  power  of  the  young  thus  produced  to  reach  the 
ratio  of  individual  survival  and  reproduction  reached  by  the  young  of 


96  ANALYSIS  OF  THE   FOUR  PRINCIPLES. 

the  pure  unions,  which  may,  therefore,  be  called  segregate  survival. 
Segregate  union  and  segregate  survival  are  forms  of  negative  segrega- 
tion ;  for  without  the  aid  of  other  influences  they  can  not  bring  the 
compatible  individuals  into  relations  producing  pure  unions. 

Segregate  union  includes  dimensional,  structural,  and  potential 
segregation,  and  it  is  of  no  small  interest  to  note  that  the  free  and 
abundant  distribution  of  the  fertilizing  elements  of  the  different  types, 
when  cooperating  with  any  one  of  these,  secures  conditions  necessary 
for  pure  unions.  This  cooperation,  therefore,  produces  positive  segre- 
gation as  truly  as  do  sexual  and  social  instincts  that  bring  together 
those  of  one  race. 

(2)  Physiological  selection  is  so  defined  and  described  by  Romanes 
as  to  include  three  of  these  eight  forms  of  impregnational  segregation. 
The  three  forms  thus  grouped  are  potential  segregation,  segregate 
fecundity,  and  segregate  vigor.  In  his  last  book  he  uses  ' '  physiolog- 
ical isolation  "  to  cover  the  same  principles  wherever  they  occur,  re- 
serving physiological  selection  for  cases  concerned  in  the  origination 
of  specific  types.*  I  greatly  prefer  the  term  physiological  isolation  to 
physiological  selection,  for  it  seems  to  me  that  selection  should  be 
used  for  the  superior  success  of  forms  that  are  both  competing  and 
freely  intergenerating,  and  not  to  designate  isolative  principles. 

(3)  Four  classes  of  self-cumulative  endowments. — Before  discussing 
these  principles  of  negative  segregation,  through  which  the  influence 
of  positive  segregation  is  greatly  increased,  it  will  be  an  advantage 
if  we  can  gain  some  idea  of  the  nature  of  cumulative  fertility  in  its 
relations  to  a  law  of  still  wider  import.  I  refer  to  the  fourfold  law  of 
antagonistic  increase  and  mutual  limitation  between  ( i )  integration, 
(2)  segregation,  (3)  adaptation,  (4)  multiplication^ — in  other  words,  be- 
tween (i)  general  invigoration  and  power  of  variation  through  cross- 
ing; (2)  opening  of  new  opportunities  and  independent  possibilities 
through  segregation ;  (3)  special  adaptation  to  present  circumstances ; 
(4)  powers  of  multiplied  individualization.  Darwin  has  considered  at 
length  the  first  and  the  third,  though  I  do  not  remember  that  he  has 
anywhere  pointed  out  that  their  development  is  due  to  a  kind  of 
self -augmentation.  I  believe  this  is  so  emphatically  the  case  that  the 
former  might  well  be  called  the  law  of  self-cumulative  vigor  and  the 
latter  the  law  of  self-cumulative  adaptation.  Corresponding  to  these 
two  laws  I  find  the  additional  laws  of  self-cumulative  segregation  and 
self-cumulative  fertility.  Darwin's  theory  that  diversity  of  natural 
selection  is  directly  and  necessarily  dependent  on  exposure  to  different 


*  See  Darwin  and  After  Darwin,  Part  III,  p.  9. 


SELF-CUMULATIVE  ENDOWMENTS.  97 

external  conditions  tends  to  obscure,  though  not  to  deny,  the  fact 
that  the  breeding  together  of  the  better  adapted  which  causes  the 
increase  of  adaptation  is  due  to  the  different  degrees  of  endowment 
in  the  organism  rather  than  to  diversity  in  the  environment.  It  is 
also  true  of  segregative  endowment  and  of  fertility  that  they  are 
necessarily  cumulative  whenever  they  both  belong  in  different  degrees 
to  members  of  the  same  intergenerant  that  are  equally  fitted.  The 
cumulation  of  vigor,  as  that  of  adaptation,  is,  I  think,  rightly  classed 
as  a  form  of  selection,  for  in  both  cases  it  depends  on  the  power  of  the 
more  highly  endowed  to  supplant  the  less  endowed  without  allowing 
them  full  opportunity  to  propagate.  The  increase  of  segregative 
endowments  and  of  fertility  when  cooperating  is  due  to  principles 
quite  different  from  this,  and  differing  from  each  other.  The  segre- 
gative endowments  augment  through  the  inherent  tendency  of  those 
more  highly  endowed  in  this  respect  to  breed  exclusively  with  those 
of  the  same  form,  and,  therefore,  in  the  long  run  to  segregate  from 
others;  while  the  fertility  of  the  more  fertile  neither  prevents  the 
individual  success  of  the  less  fertile  nor  holds  the  two  classes  apart, 
but  simply  multiplies  the  offspring  of  the  more  fertile,  making  it  sure 
that  in  each  generation  they  will  predominate. 

But  all  these  forms  of  augmentation  correspond  in  that  they  secure 
the  breeding  together  of  those  possessing  higher  degrees  of  the  special 
endowment,  and  so  increase  the  average  endowment,  either  of  the 
whole  number  of  the  offspring  or  of  the  segregated  portion.  Vigor 
increases  through  the  breeding  together  of  the  more  vigorous,  result- 
ing from  their  overcoming  and  crowding  out  the  less  vigorous  without 
allowing  them  full  opportunity  to  propagate,  though  they  are  adapted 
to  conditions  lying  in  the  environment.  Adaptation  increases 
through  the  breeding  together  of  the  better  adapted,  resulting  from 
the  failure  of  the  less  adapted  individuals  to  live  and  thrive.  Segre- 
gative endowments  increase  through  the  breeding  together  of  the  more 
highly  endowed,  resulting  from  the  fact  that  as  long  as  segregation  is 
incomplete  more  than  half  of  each  generation  of  pure  descent  are 
necessarily  the  offspring  of  parents  whose  segregative  endowments 
were  above  the  average.  Fertility  increases  through  the  breeding 
together  of  the  more  fertile,  resulting  from  the  fact  that  more  than 
half  of  each  generation  are  the  offspring  of  parents  of  more  than 
average  fertility.  Among  those  that  are  equally  adapted  to  the  envi- 
ronment the  ratio  of  propagation  varies  directly  as  the  ratio  of  fer- 
tility. This  propagation  according  to  degrees  of  fertility  is  what  I  call 
the  law  of  cumulative  fertility,  through  fecundal  selection.  It  is  not 
due  to  different  degrees  of  success,  or  to  any  advantage  which  the 


98  ANALYSIS  OF  THE  FOUR  PRINCIPLES. 

individuals  of  one  form  have  over  those  of  other  forms,  but  simply  to 
the  higher  ratio  of  multiplication  in  the  more  fertile  forms  securing  the 
intergeneration  of  the  more  fertile.  Fecundal  selection  cooperating 
withnatural  selection  insures,  in  the  descendants,  the  predominance  of  the 
better  adapted  of  the  more  fertile,  and  the  more  fertile  of  the  better  adapted. 
(4)  Partial  positive  segregation  may  be  greatly  strengthened  by  coope- 
rating negative  segregation. — It  seems  to  be  a  fundamental  law  that 
vigor  and  variation  in  the  offspring  depend  on  some  degree  of  diversity 
of  constitution  in  the  parents,  and  diversity  of  constitution  that  is  not 
entirely  fluctuating  depends  on  some  degree  of  positive  segregation; 
therefore  vigor  and  variation  depend  on  the  breaking  down  of  incip- 
ient segregations  and  on  the  interfusion  of  the  slightly  divergent 
forms  that  had  been  partially  segregated.  But  in  the  history  of  every 
race  that  is  winning  success  by  its  vigor  and  variation  there  is  liable  to 
come  a  time  when  some  variety,  inheriting  sufficient  vigor  to  sustain 
itself,  even  if  limited  to  the  benefits  of  crossing  with  the  individuals  of 
the  same  variety,  becomes  partially  segregated.  As  we  have  already 
seen,  when  positive  segregation  is  correlated  with  segregate  fecundity, 
the  segregated  types  tend  to  become  more  and  more  dominant  in 
number;  but,  in  the  very  nature  of  things  not  only  will  the  segrega- 
tion be  for  many  generations  only  partial,  but  partial  segregation — 
unless  it  is  aided  by  some  other  principle — although  it  may  greatly 
delay  the  submerging  of  different  groups  in  one  common  group,  will 
never  prevent  that  result  being  finally  reached.  Though  the  siphon 
which  connects  two  tanks  of  water  be  ever  so  small,  the  water 
will  in  time  find  a  common  level  in  both  tanks,  unless  there  are 
additions  or  subtractions  of  water  that  prevent  such  a  result.  So, 
in  the  case  under  consideration,  final  fusion  will  take  place,  unless 
differentiation  progresses  more  rapidly  than  the  fusion,  or  some  other 
influence  comes  in  to  counteract  the  leveling  influence  of  occasional 
crosses.  If,  under  such  conditions,  some  branch  of  the  partially  segre- 
gated variety  becomes  more  fertile  when  generating  with  members  of 
the  same  variety,  and  less  fertile  when  generating  with  other  varieties, 
a  principle  will  be  introduced  tending  to  strengthen  any  form  of 
partial  segregation  that  already  exists  between  the  varieties.  This 
cooperation  of  segregate  fecundity  with  partially  segregative  endow- 
ments will  produce  pure  masses  of  each  variety,  when,  without  the 
action  of  this  principle,  all  distinctions  would  be  absorbed  by  the 
crossing.  We  know  that  a  transition  from  integrate-  fecundity  to 
segregate  fecundity  usually  takes  place  at  a  point  in  the  history  of 
evolution  intermediate  between  the  formation  of  an  incipient  variety 
and  a  strongly  marked  species ;  and  though  the  causes  that  produce 


COOPERATION  OF  POSITIVE  AND  NEGATIVE  SEGREGATION.         99 

this  transition  may  be  very  difficult  to  trace,  I  believe  that  the 
results  that  must  follow  can  be  pointed  out  with  considerable  clear- 
ness and  certainty. 

Darwin's  investigations  have  shown  that  in  many  cases,  if  not  in  the 
majority,  the  relation  of  varieties  to  each  other  is  that  which  I  have 
called  "integrate  fecundity"  and  "integrate  vigor";  that  is,  the 
highest  fertility  is  attained  when  varieties  are  crossed  and  the  vigor 
of  offspring  thus  produced  is  greater  than  when  the  intergeneratiori  is 
within  the  limits  of  one  variety.  He,  however,  gives  in  Variation 
under  Domestication,  chapter  xvi,  some  special  cases,  in  which 
* '  varieties  of  the  same  species  behave  when  crossed  like  closely  allied 
but  distinct  species,"  and  remarks  that  similar  cases  "may  not  be  of 
very  rare  occurrence ;  for  the  subject  has  not  been  attended  to."  The 
same  cases  are  also  mentioned  in  all  the  editions  of  the  Origin  of 
Species.* 

(5)  Negative  segregation  unaided  by  positive  segregation  tends  to  ex- 
tinction.— -The  problems  that  arise  in  considering  the  different  results 
produced  by  different  degrees  of  positive  segregation  and  segregate 
fecundity  are  of  a  nature  suitable  for  mathematical  treatment.  Be- 
fore, however,  computing  the  effects  of  segregate  fecundity  when 
cooperating  with  positive  segregation,  it  will  be  in  place  to  show  that 
it  is  of  itself  only  a  negative  form  of  segregation,  having  no  power  to 
insure  the  propagation  of  varieties  thus  characterized,  though  they  are 
fully  adapted  to  the  environment.  This  is  most  easily  brought  to 
light  by  considering  the  effect  of  a  high  degree  of  this  quality  when 
positive  segregation  is  entirely  wanting,  or  when  it  is  sufficient  to  give 
simply  a  chance  of  segregate  breeding  by  bringing  each  individual  near 
to  its  natural  mate.  For  example,  let  us  suppose,  first,  that  a  male 
and  a  female  each  of  several  allied  but  mutually  sterile  species  are 
brought  together  on  one  small  island,  all  tendencies  to  positive  segre- 
gation being  removed,  while  mutual  sterility  still  remains;  second, 
that  a  male  and  female  when  once  mated  remain  together  for  the 
breeding  season;  and,  third,  that  all  find  mates.  Now,  if  we  have 
seven  species  each  represented  by  one  individual  of  each  sex,  what 
is  the  probability  that  all  the  species  will  be  propagated?  And  what 
the  probability  for  the  propagation  of  none,  or  of  but  one,  or  of  but 
two,  or  of  but  three  of  the  species?  The  answers,  as  I  have  computed 
them,  are  as  follows :  The  probability  that  none  will  be  propagated  is 
^ ;  that  I  species  will  be  is  5^ ;  that  2  species,  ^ ;  that  3  species, 
S;  that  4  species,  J5;  that  5  species,  ^i  that  7  species,  ^.     These 


♦  See  first  edition,  p.  238;  fifth  edition,  p.  259;  sixth  edition,  p.  258. 


lOO  ANAI.YSIS  OF  THE   FOUR   PRINCIPI<ES. 

numerators  are  found  in  the  seventh  Une  of  a  table  of  figures 
which  I  call  the  " permutational  triangle."*  If  we  have  ten  species, 
the  probability  that  in  any  one  trial  no  species  will  match  truly  and 
be  propagated  is  Hi^;  that  i  species  will  match  truly  and  prop- 
agate is  ^^^ ;  that  lo  will  is  3^.  This  means  that  if  3,628,800  trials 
are  made,  i  of  them  will  probably  be  a  case  in  which  each  male 
pairs  with  the  female  of  the  same  species,  while  1,334,961  will  be 
cases  in  which  none  are  so  matched,  and  1,334,960  will  be  cases  in 
which  one  pair  is  so  matched.  It  therefore  appears  that  more  than 
Yi  of  the  probabilities  are  against  the  continuance  of  more  than  one 
qf  the  ten  species. 

It  is  not,  however,  necessary  to  have  a  complete  solution  of  this 
problem  in  order  to  reach  the  conclusion  that  the  origin  of  separate 
races  and  species  depends  not  only  upon  their  adaptation  to  the  en- 
vironment and  their  mutual  sterility  when  crossing  with  each  other, 
but  also  upon  their  positive  segregation.  We  can  further  see  (when 
considering  an  extreme  case,  like  either  of  the  above-supposed  cases) 
that  segregate  fecundity,  without  the  aid  of  positive  segregation,  must 
lead  to  extinction.  We  have  already  seen  that  partial  positive  segre- 
gation can  not  by  itself  prevent  the  fusion  of  species.  It  therefore 
follows  that  in  order  to  account  for  the  continuance  of  divergent  races 
we  must  suppose  either  that  the  positive  segregation  is  complete  or 
that  the  divergent  evolution  is  strong  enough  to  more  than  counter- 
balance the  influence  of  the  occasional  crossing,  or  that  the  partial 
positive  segregation  is  aided  by  segregate  fecundity,  or  by  some  other 
form  of  segregate  survival. 

(6)  Partial  positive  segregation  unaided  by  negative  segregation  can  not 
prevent  fusion. — Between  the  members  of  species  belonging  to  different 
orders  we  find  not  only  complete  segregation,  but  complete  sterility 
when  attempts  at  crossing  are  made ;  but  hope  of  gaining  an  explana- 
tion of  how  these  characteristics  have  arisen  is  found,  not  in  the  study 
of  those  cases  in  which  the  process  has  been  completed,  but  in  the 
study  of  the  relations  to  each  other  of  species  and  varieties  that  are 
characterized  by  segregation  and  mutual  sterility,  that  is,  not  com- 
plete. Here,  again,  mathematical  analysis  will  help  us  in  understand- 
ing the  subject.  Though  I  have  not  succeeded  in  constructing  a  com- 
plete mathematical  representation  of  all  the  grades  of  intermingling 
that  will  take  place,  I  have  found  a  general  formula  that  gives  a  close 
approximation  to  the  proportion  in  which  two  species  will  produce 
pure-breeds  as  contrasted  with  the  proportion  of  cross-breeds  that 

*  See  Appendix  II  of  this  volume. 


LESS   COMPETITION,  WITH   ESCAPE   FROM   ENEMIES.  lOI 

will  be  produced  in  any  case  in  which  the  degree  of  segregation  and 
the  ratios  of  fertility  for  the  pure  and  crossed  breeds  are  known. 

Taking  formula  (4),  reached  a  little  below  (on  page  105),  it  will 
be  seen  that  if  M  =  m,  that  is,  if  cross-breeds  are  as  fertile  as  pure- 
breeds,  the  ratios  of  cross-breeds  to  pure-breeds  increases  with  each 
generation,  and  in  time  the  pure-breeds  will  be  overwhelmed. 

14.  Segregate  Freedom  from  Competition  and  Segregate  Escape  from  Enemies. 

Before  leaving  the  subject  of  segregate  survival  it  may  be  well  to 
give  an  illustration  of  the  effects  of  these  two  forms  of  the  principle 
when  cooperating  with  industrial  and  social  segregation.  On  certain 
of  the  South  Pacific  islands  there  are  found  two  species  of  rats  occupy- 
ing the  same  areas;  but  one  species  has  strong  legs  and  claws  fitted 
for  climbing  the  trees  which  they  inhabit,  while  the  other  species  lives 
on  the  ground  and  has  limbs  fitted  for  its  separate  sphere  of  activities. 
As  the  latter  is  the  prevalent  type  on  surrounding  groups  of  islands, 
there  seems  to  be  good  reason  for  believing  that  the  tree  species  was 
derived  from  the  ground  species. 

Let  us  now  consider  some  of  the  conditions  that  might  easily  arise 
in  the  formation  of  such  a  species.  Let  us  first  suppose  that  there 
arises  a  period  of  scarcity  in  which  the  ordinary  food  of  the  species  is 
obtained  with  difficulty,  while  on  the  trees  are  to  be  found  either 
fruits  which  are  more  or  less  accessible  to  a  good  climber,  or  perhaps 
snails,  which  in  tropical  regions  live  constantly  on  the  trees  of  the 
dense  forests.  Again,  let  us  suppose  that  the  ordinary  rat  of  the  orig- 
inal stock  finds  his  strength  sufficient  to  enable  him  to  spend  only 
one-tenth  of  each  day  seeking  food  in  the  trees,  and  that  accordingly 
he  can  do  better  by  remaining  on  the  ground;  but  there  are  a  very 
few  individuals,  say  one  in  a  thousand,  who  are  able  to  spend  one- 
quarter  of  their  time  in  climbing ;  and  for  them  there  is  abundance  of 
food,  which  induces  them  to  spend  most  of  their  time  in  the  trees. 
These  few  find  holes  in  the  trees,  where  they  congregate  during  hours 
of  rest,  and  thus  become  more  or  less  segregated  from  the  rest  of  the 
species. 

Again,  let  us  assume  that  half  of  these  rats  feeding  in  the  trees  are 
of  variation  a,  with  instincts  leading  them  to  spend  one-half  of  their 
time  in  the  trees  and  one-half  of  their  time  on  the  ground,  the  result 
being  that  one-half  of  them  form  cross  unions  and  have  their  nests  on 
the  ground,  while  one-half  of  them  pair  with  tree-feeding  rats  and 
have  their  nests  on  the  trees.  Further,  let  us  assume  that  the  fertility 
of  the  pure-breeds  and  half-breeds  is  the  same,  each  pair  producing 
about  80  young  during  their  life.     Therefore,  the  multiplier  for  the 


I02  ANALYSIS  OF  THE   FOUR  PRINCIPtES. 

pure-breeds,  which  in  my  tables  is  represented  by  M,  is  40;  and  the 
raultipUer  for  the  half-breeds  is  also  40,  i.  e.,  ni  -^  40.  And  once  more, 
let  us  assume  that  of  the  cross-breeds  which  have  their  homes  on 
the  ground  with  the  original  stock  only  i  in  40  reaches  maturity; 
that  is,  on  account  of  the  number  of  their  enemies  and  the  severity  of 
the  competition  for  food,  their  real  multiplier,  after  all  the  conditions 
of  survival  have  had  a  chance  to  operate,  is  40  x  ^'0  =  1.  In  other 
words,  the  original  stock  and  the  half-breeds  mingled  with  them  are 
simply  able  to  hold  their  own,  without  any  continuous  increase.  On 
the  other  hand,  the  arboreal  group  are  so  free  from  enemies  and  so 
well  provided  with  food  that  three-fourths  of  them  come  to  maturity, 
and  their  multiplier  when  corrected  is  40  x  |  =  30. 

Let  us  assume  that  the  other  half  of  these  rats  feeding  on  the  trees 
are  of  the  variation  b,  with  instincts  leading  them  to  spend  one-third 
of  their  time  on  the  ground,  and  accordingly  one-third  of  them  mate 
with  the  original  stock  and  have  their  nests  on  the  ground.  As  in  the 
case  of  variation  a,  the  multiplier  for  pure  arboreal  breeds  is  30  and 
for  cross-breeds  is  i . 

Let  us  now  suppose  that  there  is  an  arboreal  colony  of  60  individ- 
uals occupying  a  forest  on  one  of  these  islands,  and  that  30  of  them 
belong  to  the  variation  a,  and  30  of  them  to  variation  b.  What  will 
be  the  number  of  pure-breed  arboreal  rats  in  the  next  generation,  and 
of  these  how  many  will  be  the  offspring  of  variation  a  and  how  many 
the  offspring  of  variation  b  ? 

Of  variation  a  one-half  cross  with  the  original  stock  and  we  have — 
Cross-breeding  offspring,  15  x  i  =  15. 
Pure-breed  offspring,  15  x  30  =  450. 

Of  variation  b,  one-third  cross,  and  we  have — 
Cross-breed  offspring,  10  x  i  =  10. 
Pure-breed  offspring,  20  x  30  =  600. 

Therefore,  in  the  next  generation  of  the  pure-breed  colony  in  the 
trees  there  will  be  i  ,050,  of  which  three-sevenths  are  offspring  of  varia- 
tion a  and  four-sevenths  are  offspring  of  variation  b.  It  follows 
that  through  hereditary  influences  the  average  instinct  for  arboreal 
life  will  be  increased ;  and  we  may  expect  it  to  continue  to  increase 
in  the  same  way  in  successive  generations. 

But  there  is  a  psychological  influence  that  will  come  in  to  exaggerate 
the  segregative  tendency.  The  1,050  rats  of  the  generation  we  have 
now  reached  have  been  reared  on  the  trees  of  the  dense  forest  or  jungle, 
where  they  may  travel  over  a  considerable  area  without  descending 
to  the  ground,  and  have  formed  the  habit  of  spending  their  whole  time 
in  the  trees,  so  that  not  i  in  100  will  mate  with  the  ground  rats;  and 


RATIOS   BETWEEN   CROSS-BREEDS   AND    PURE-BREEDS.  IO3 

in  a  few  more  generations  this  ratio  will  become  only  i  in  i  ,000,  or 
I  in  many  thousands.  Under  such  conditions  the  arboreal  variety 
will  soon  develop  a  manner  and  movement  by  which  they  recognize 
each  other ;  and  their  social  instincts  will  lead  them  to  band  together 
in  driving  away  the  rare  intruders  from  the  ground  who  venture  to 
invade  their  sphere  of  influence.  Their  isolation 'from  the  original 
stock  may  thus  become  complete  in  the  course  of  a  few  generations, 
and  that,  too,  without  any  action  of  the  principles  of  segregate  fecun- 
dity and  segregate  vigor;  that  is,  without  the  cooperation  of  any  form 
of  what  Romanes  has  called  "  physiological  segregation." 

Segregate  freedom  from  competition  and  segregate  escape  from  ene- 
mies favor  segregation  in  the  earlier  stages  of  newly  adopted  methods 
of  life,  and  so  tend  to  exaggerate  the  importance  of  slight  changes 
attained  by  the  first  stages  of  divergent  forms  of  environal  selection. 
When  the  new  colony  has  so  multiplied  as  to  appropriate  nearly  all  the 
newly  opened  resources,  competition  will  again  become  an  important 
factor,  and  by  that  time  the  gradual  appearance  of  segregate  fecun- 
dity and  segregate  vigor  may  fortify  the  new  type  against  being 
swamped  by  crossing.  Segregate  adaptation  is  also  an  important 
factor  cooperating  in  the  whole  process.  So  the  five  principles  of 
segregate  survival  are  found  to  sustain  and  supplement  each  other  in 
producing  divergent  evolution. 

15.  Computation  of  the  Ratio  of  Cross-breeds  to  Pure-breeds,  under 
Given  Ratios  of  Mixed  Unions  and  of  Fertility. 

It  will  simplify  the  problem  if  individuals  of  different  degrees  of 
crossed  descent  are  classed  together  and  compared  with  those  of  pure 
descent.  It  will  also  be  a  convenience  to  make  M  —  the  multiplier 
that  represents  the  influence  of  all  the  conditions  of  survival  for  those 
of  pure  descent,  and  m  —  the  multiplier  that  represents  the  influence 
of  all  the  conditions  of  survival  for  those  of  mixed  descent.  A  =  the 
initial  number  of  the  new  variety ;  c  —  the  fraction  that  represents 
the  proportion  of  the  pure-breed  individuals  that  form  cross-unions; 
and  P  —  the  whole  number  of  individuals  of  pure  descent.  C  —  the 
whole  number  of  individuals  of  cross  descent. 

It  may  be  observed  that  a  problem  of  completely  parallel  terms  will 
be  obtained  if  we  make  A  =  an  initial  number  of  dollars  left  as  an 
endowment  to  draw  compound  interest  for  many  years ;  c  =  a  rate 
of  taxation  corresponding  in  its  periods  with  the  periods  for  estimat- 
ing interest,  the  avails  of  this  taxation  being  kept  for  another  institu- 
tion. M  -  the  multiplier  by  which  we  obtain  the  principal  plus  the 
interest  remaining  in  the  endowment ;  m  =  the  multiplier  by  which 


104  ANALYSIS   OF  THE  FOUR   PRINCIPLES. 

we  obtain  the  principal  plus  the  interest  allowed  on  the  money  with- 
drawn by  taxation ;  P  —  the  whole  value  of  the  endowment  at  the 
end  of  a  given  number  of  periods;  C  ==  the  whole  of  the  money  with- 
drawn by  taxation  and  subjected  to  a  separate  rate  of  interest,  down 
to  a  given  period.*  It  should  be  observed  that,  as  in  the  bionomic 
problem  M  and  m  are  liable  to  become  fractions  less  than  i ,  so  also  in 
the  problem  of  money  investment  either  of  these  factors  may  fall 
below  I.  This  is  the  case  when  the  charges  for  management,  etc.,  are 
more  than  the  interest. 

Table  giving  Formulas  for  the  Ratios  between  Cross-breeds  and  Pure-breeds. 

In  third  generation,  P  —  A  (A/  —  Mc)^  =  pure-bred  individuals  in 
the  third  generation. 

In  nth  generation,  P  =  A  (M  —  Mc)"  =  pure-bred  individuals  in 
the  wth  generation. 

C  =  the  number  of  cross-bred  individuals  in  any  generation. 
In  first  generation: 

C  =  Acm 
In  second  generation: 

C  =  A  cm^  +  >lcw  (M  -  Mc) » 
In  third  generation: 

C  =  Acm^  +  A cm^  (M  -  Mc) ^  +  Acm{M-  Mc)^ 

-Acm{M-Mcy\^    lAr=Arcj   +  {M=Mc\    ^'] 
In  nth  generation : 


i^M-McJ 


+  1 


In  third  generation : 


C  mc  f   r       m       V  .    r      m       1  »  ,       \ 

P^M-Mc^'X   \m-Mc^^    "^  [M-McJ         ^  j 


*  The  method  by  which  the  first  steps  are  made  in  reaching  the  desired  formula 
will  be  understood  by  considering  this  endowment  problem.  The  advantage  of 
the  formula  here  reached  is  that  it  gives  the  ratio  of  all  the  cross-breeds  to  pure- 
breeds,  and  not  simply  of  half-breeds  to  pure-breeds,  as  was  the  case  in  the  formula 
reached  in  my  paper  on  Divergent  Evolution  (see  Appendix  I). 

t  This  is  obtained  by  dividing  each  term  of  the  second  member  of  the  previous 
equation  by  Acm  {M  —  Mc)'-,  and  then  placing  the  same  amount  as  amultipher 
outside  of  brackets. 


TABLE   A. 


105 


In  nth  generation : 

c  _    mc      j  r     m     1  **~' 1    /\3    r     m    ^^ 


+ 


r    w    1 1,    "I 

[m-McJ  / 

As  the  sum  of  the  above  progression  within  the  brackets  is  found 
by  the  formula  5  =  z :.  in  which  a  =  i  and  r  = 


and 


mc 


C_        

P    M-Mc 


I  — 

111    WllUJll  t 

I 

m 

M-Mc 

mc 

mc 


M  —  Mc 
M-Mc 


M-Mc    M  —  Mc  —  m 


P     M  —  Mc  —  m 


C  =  P^ 


wc 


M  —  Mc  —  m 


=  Formula  (3)  ;* 


=  Formula  (4)  ; 


Table  A. 

[From  Formula  (4).] 


WhenAf  =  10 

and  m  - 

9. 

8. 

7. 

6. 

5. 

4. 

3. 

2. 

1. 

li  c  —  y  then  cross-breeds) 
—  pure-breeds  X             j 

9 

8 

7 

6 

5 

4 

3 

2 

1 

-  8 

-6 

-4 

-2 

0 

2 

4 

6 

8 

If  c  r^  i  then  C  =  P  X 

9 

—  7 

8 
—  4 

7 
-  1 

6 
2 

5 
5 

4 
8 

3 
11 

2 
14 

I 
17 

If  c  =  i,  then  C  =  P  X 

9 
-6 

8 
—  2 

7 
2 

6 
6 

5 
10 

4 

14 

3 
18 

2 
22 

1 
26 

If  c  =  ^    then  C  =  P  X 

9 

—  5 

8 
0 

7 
5 

6 

16 

5 
15 

4 
20 

3 
25 

2 
30 

1 
35 

li  c  =  1.  then  C  ^  P  X 
6 

9 
—  4 

8 
2 

7 
8 

6 
14 

5 
20 

4 
26 

3 
32 

2 
38 

1 
44 

If  c  =    y    then  C  =  P  X 

9 
0 

8 
16 

7 
20 

6 
30 

5 
40 

4 

50 

3 
60 

2 
70 

1 
80 

If  c  =4.  then  C=.PX 

9 
90 

8 
190 

7 
290 

6 
390 

5 
490 

4 
590 

3 
690 

2 
790 

1 
890 

"'^  =  roW*''^"^  =  ''^ 

9 
990 

8 
1990 

7 
2990 

6 
3990 

5 
4990 

4 
5990 

6990 

2 
7990 

1 

8990 

*  Formulas  (i)  and  (2)  were  given  in  my  paper  on  Divergent  Evolution  (see 
Appendix  I). 


io6 


ANALYSIS  OF  THE   FOUR  PRINCIPLES. 


Method  of  Testing  Table  A. 

I  C       7 

Let  M=  lo;  m  =  y;   c  =  -;  then^=-  according  to  the  table. 

We  now  place  under  pure-breeds  any  number,  and  under  cross- 
breeds 2)h  times  that  number. 


Pure-breeds. 

Cross-breeds. 

C 
P 

In  «th  generation,                                       2 

In  nth  generation, 

7 

7 

2 

(w+ i)th     "            =.  2(M  — Mc)'^  15 

In  («-f-  i)th  gen., 

49 

■>^l 

7 
2 

(n-f  2)th     "    )        i       2(7.5)^  ) 
^2iM-Mcy    )        i=2is6.\)  ) 

'  =343  +  24i-|-  261 

'r 

393i 

_7 

2 

Starting  with  the  fraction  -,  given  in  Table  A,  as  correct  for  the 

C      7 
nth  generation,  we  find  that  p=r  -^  is  correct  for  all  subsequent  gene- 
rations ;  and  this  proves  the  formula  to  be  correct. 

C 

If  the  denominator  of  the  fraction  representing  the  value  of  =  is 

o,  or  less  than  o,  the  disproportion  increases  with  each  generation ; 
that  is,  cross-breeds  become  the  overwhelming  element. 

In  this  case  by  which  we  are  testing  the  correctness  of  Table  A, 
suppose  the  pure-breeds  to  be  2  and  the  cross-breeds  to  be  7  in  the 
generation  with  which  we  commence.  In  the  next  generation,  which 
we  designate  as  the  (n  +  i)th  generation,  the  pure-breeds  will   be 

2  X  (M  —Mcy  =  2  I  10—    -  I  =  15.      In  the  (w  +  2)th  generation 

I  4  J 

the  pure-breeds  ^  2  X  (M  -  Mcy  =  2  x  (7.5)^  -=  11 2.5. 

The  cross-breeds  in  the  (n  +  i)th  generation  =  7  x  the  cross- 
breeds of  the  previous  generation,  plus  7  X  one-quarter  of  the  pure- 
breeds  of  the  previous  generation  =  7^  +  -.  In  the  (n  +  2)th  gen- 
eration the  cross-breeds  wilj^'be  7  x  the  cross-breeds  of  the  (n  x  i)th 
generation,  plus  7  x  one-quarter  of  the  pure-breeds  of  the  (w  +  i)th 


generation  =  7-^  +  —  +  ' 


>"  7 


393-75- 


USE  OF   THB   TABLES.  I07 

16.   The  Use  of  the  Tables. 

The  first  object  of  this  computation  is  to  show  that  a  partial  posi- 
tive segregation  that  is  ineffectual  in  preserving  a  new  variety  from 
the  swamping  effects  of  crossing  becomes  very  effectual  when  a  mod- 
erate degree  of  segregate  fecundity  cooperates  with  it.  It  should  be 
observed  that  when  considering  partial  segregation  cooperating  with 
segregate  fecundity  I  assume  that  the  two  varieties  that  are  compet- 
ing on  the  same  area  are  equally  adapted  to  the  environment,  and 
that  the  action  of  other  principles  is  equal  in  each,  in  order  that  I  may 
compute  the  effects  of  the  two  factors  under  consideration  when  free 
from  disturbing  influences.  It  has  been  objected  that,  according  to 
my  Table  I,*  the  eighteenth  generation  is  many  thousand  times  larger 
than  the  initial  number,  which  is  not  the  usual  result  under  the  condi- 
tions surrounding  natural  varieties.  In  reply  I  would  say  that  even 
in  natural  varieties  it  is  not  at  all  impossible  that  the  number  should 
double  with  each  generation  for  at  least  a  few  generations!  especially 
when  a  variety  has  gained  the  use  of  resources  heretofcS'e  unused, 
and  that  for  the  purpose  of  showing  the  ratio  in  which  half-breeds  and 
pure-breeds  stand  to  each  other  it  is  entirely  immaterial  whether  we 
assume  that  the  number  that  arrive  at  maturity  are  the  same  in  each 
generation,  or  that  each  successive  generation  is  nearly  double  that  of 
the  preceding  generation. 

But  does  not  the  assumption  that  the  ratio  of  cross-breeding  re- 
mains the  same  in  successive  generations  vitiate  the  whole  computa- 
tion and  render  it  worthless?  I  think  not.  My  contention  is  that 
when  segregate  fecundity  comes  to  the  aid  of  such  a  principle  as  pre- 
potential  segregation  (which  is  only  partial  in  its  action,  and  therefore 
by  itself  unable  to  prevent  swamping),  the  result  is  the  progressive 
action  of  both  principles  in  each  successive  generation.  But  before 
we  can  show  how  this  cumulative  action  arises  we  must  have  some 
formula  for  showing  the  natural  result  of  any  given  degree  of  segre- 
gation combined  with  a  given  degree  of  segregate  fecundity ;  and  the 
proper  formula  for  this  purpose  seems  to  be  the  result  that  would  be 
reached,  if  the  principles  should  continue  at  the  given  degrees  for  a 
considerable  number  of  generations. 

Take  for  example  the  case  represented  in  Table  I.*  What  is  the 
ratio  between  half-breeds  and  pure-breeds  that  most  truly  represents 
the  case  ?     Shall  we  go  to  the  end  of  the  first  generation  and  say  that, 

p  =  Y^,  or  go  to  the  eighteenth  generation  and  find  that  p  —  z~^ 


*  See  my  paper  on  Divergent  Evolution,  Appendix  I. 


lo8  ANALYSIS  Olf  THE  FOUR  PRINCIPLES. 

Undoubtedly  the  latter  is  the  one  we  need  to  represent  the  result 
toward  which  the  given  conditions  tend,  though  before  the  eighteenth 
generation  is  reached  the  degree  of  segregate  breeding  will  have 
become  more  stringent. 

Having  obtained  a  formula  giving  the  results  that  would  be  reached 
if  the  ratios  of  cross-breeding  and  of  attendant  infertility  were  con- 
tinued at  a  given  level  for  a  number  of  generations,  we  next  inquire 
whether  there  is  any  reason  to  believe  that  the  degrees  of  segregate 
breeding  will  become  more  stringent  in  successive  generations,  and 
whether  the  infertility  of  cross-breeds  will  be  increased. 

17.  Cumulative  Segregation  Resulting  from  Segregative  Endowments. 

Let  us  consider  a  partially  segregated  variety  of  a  plant  species  in 
which  there  is  some  variation  in  the  segregative  endowments.  We 
will  suppose  that  the  species  is  one  whose  pollen  is  freely  distributed 
by  the  wind  and  whose  stigma  is  susceptible  of  fertilization  for  ten 
hours. 

Though  the  individuals  of  the  new  and  partially  segregated  variety 
are  very  few  as  compared  with  the  original  stock,  yet  the  pollen  of  the 
new  kind  reaches  every  stigma  of  the  same  kind  before  the  ten  hours 
of  its  susceptibility  have  passed,  while  pollen  of  the  original  kind,  be- 
ing far  more  abundant,  is  sure  to  reach  every  stigma  soon  after  their 
flowers  have  opened. 

The  positive  segregation  of  the  new  variety  we  will  suppose  is  se- 
cured by  prepotence  of  the  pollen  of  the  variety  on  the  stigmas  of  the 
same  variety,  one  variation  being  prepotent  for  about  five  hours, 
with  the  result  that  one-half  of  the  individuals  breed  pure  and  one-half 
are  crossed ;  that  is,  c  =  ^ ;  while  another  variation  is  prepotent  for 
about  6§  hours,  with  the  result  that  two-thirds  of  the  individuals 
breed  pure  and  one-third  are  crossed ;  that  is  c  =  ^. 

The  negative  segregation  of  the  new  variety  we  will  suppose  is  se- 
cured by  segregate  survival;  for  the  pure-breeds,  through  different 
degrees  of  adaptation  to  the  new  station,  enjoy  different  degrees  of 
success  in  leaving  offspring  that  come  to  maturity,  the  less  adapted 
variations  being  multiplied  by  i  in  each  generation,  and  the  better 
adapted  multiplied  by  2  in  each  generation,  while  the  cross-breeds 
are  so  lacking  in  adaptation  as  to  be  multiplied  by  }  in  each  genera- 
tion. We  therefore  have  two  values  for  M,  each  occurring  under 
c  =  ^,  and  again  under  c  =  J.  In  one  variation  we  have  M—i,  and 
m  =  4,  the  proportion  being  as  M  ~  10,  and  w  ==  2  ;  and  in  the  other 
variation  we  have  M  =  2,  and  m  =  ^,  the  proportion  being  as  M  =  10 
and  m  =1. 


CUMULATIVE  SEGREGATION  THE   RESULT.  109 

Solution  reached  by  means  of  Table  V. — Looking  in  Table  V,*  we  find 
that  when  c  =  ^,  and  M  -=io, 

(var.  i)  then  with  m  =  2,  half-breeds  =  pure-breeds  x  A; 

(var.  2)  and  with  m  —  i,  half-breeds  ~  pure-breeds  x  ^; 
that  when  c  ~  ^,  and  M  =  10, 

(var.  3)  then  with  w  =  2,  half-breeds  =  pure-breeds  X  2_; 

(var.  4)  and  with  m  =  1,  half-breeds  =  pure-breeds  x  ^. 
Now,  it  is  evident  that  the  influence  on  the  next  generation  of  the 
variation  marked  as  var.  4,  which  is  the  most  highly  segregated,  will 
be  much  greater  than  that  of  any  other  one  of  the  variations. 

Solution  reached  by  means  of  Table  A. — If  we  consult  Table  A,  we 
shall  find  an  equal  contrast,  for  it  gives  for 

(var.  i)  cross-breeds  =  pure-breeds  x  |^; 

(var.  2)  cross-breeds  =  pure-breeds  x  i; 

(var.  3)  cross-breeds  =  pure-breeds  X  1 ; 

(var.  4)  cross-breeds  =  pure-breeds  x  1. 
Solution  reached  by  direct  computation. — A  similar  conclusion  may 
be  reached  by  computing  the  result  for  a  few  generations.  Let  us 
suppose  that  for  one-half  of  the  new  variety  the  average  prepotence 
allows  one-half  of  the  individuals  to  form  cross-unions,  and  that  for 
the  other  half  of  the  variety  the  average  prepotence  allows  only  one- 
third  of  the  individuals  to  form  cross-unions ;  and  also  that  one-half  of 
each  of  these  variations  is  so  adapted  as  to  multiply  by  2  in  each 
generation,  while  the  other  half  multiplies  by  i.  As  in  the  previous 
computation  cross-breeds  are  niultiplied  by  4-  in  each  generation. 
Let  us  now  assume  that  in  a  given  generation  there  are  1,000  indi- 
viduals in  each  of  these  variations,  and  what  will  be  the  number  of 
pure-breeds  of  each  of  the  four  variations  that  will  come  to  maturity 
in  the  next  generation,  and  what  the  number  of  cross-breeds? 
In  var.  i,  c  =  7},  M  =  i,  w  =  ^;  (i,  e.,  pure -breeding  500;  crossing 

500),  .'.  pure-breeds  500;  half-breeds  100. 
In  var.  2,  c  =  ^,  M  =  2,  m  =  i;  (i.  e.,  pure-breeding  500;  crossing 

500),  .'.  pure-breeds  1,000;  half-breeds  100. 
In  var.  3,  c  =  j,  M  =  i,  w  =  4  ;  (i.  e.,   pure-breeding  666;   crossing 

333)»  •'•  pure-breeds  666;  half-breeds  66. 
In  var.  4,  c  -  ^,   M  =  2,  m  =  4;  (i.  e.,  pure-breeding  666;  crossing 

333)t  •'•  pure-breeds  1,332;  half-breeds  66. 
The  sum  of  the  pure-breeds  of  all  the  variations  3,498. 
It  will  be  observed  that  in  one  generation  the  pure-breeds  have 
decreased  from  4,000  to  3,498;  that  is,  their  numbers  have  dimin- 


*  See  my  paper  on  Divergent  Evolution,  Appendix  I. 


no  ANALYSIS  OI^  THE   FOUR   PRINCIPLES. 

ished  one-eighth.  In  the  second  generation  the  result  will  be  quite 
different ;  for  variations  2  and  4  already  constitute  two-thirds  of  the 
whole  number  of  pure-breeds. 

Second  Generation—  Pure-breeds. 

Of  variation  i  .......  .  250 

Of  variation  2  .  .  .  .  .  .  .  .        i ,  000 

Of  variation  3  .......  .  444 

Of  variation  4  ........        1,776 


3,470 
In  this  generation  the  decrease  is  onh^  28  individuals,  or  about  ~. 

Third  Generation —  Pure-breeds. 

Of  variation  i  .          .          .          .          .          .          .  125 

Of  variation  2  .          .          .          .          .          .          .  •        i ,  000 

Of  variation  3  .......  .            296 

Of  variation  4  .          .          .          .          .          .          .  .        2,368 


3,789 
In  this  generation  there  is  an  increase  of  3 1 9  individuals,  or  a  little 


over 


Fourth  Generation —  Pure-breeds. 

Of  variation  i  .......  .             62 

Of  variation  2  .          .          .          .          .          .          .  •        i ,  000 

Of  variation  3  .          .          .          .          .          .          .  .            198 

Of  variation  4  .          .          .          .          .          .          .  "     .       3,  156 


4,416 
In  this  generation  there  is  an  increase  of  627,  or  of  nearly^. 

Tenth  Generation —  Pure-breeds. 

In  variation  i  .          .          .          .          .          .          .                    0.98 

In  variation  2  .          .          .          .          .          .          .          •        i ,  000 

In  variation  3  .          .          .          .          .          .          .          .              16 

In  variation  4  ........      17,758 

18,775 
Var.  4,  of  Tenth  Generation  =  1,000  (1.3333 J)'"  computed  by  logarithms. 

We  therefore  observe  that  in  the  tenth  generation  variation  i  has 
become  less  than  i ,  and  variation  4  has  become  the  predominant  type. 

For  the  next  ten  generations  the  average  positive  segregation  will  be 
advanced,  (i)  by  the  preponderance  of  variation  4,  and  (2)  by  the 
fact  that  the  new  variety  occurs  in  much  larger  masses  than  at  the 
beginning  of  the  computation,  and  will  therefore  be  less  exposed  to 
cross-fertilization. 

Now  that  the  mass  of  pure-breeds  is  increased  more  than  fourfold, 
it  is  reasonable  to  suppose  that  the  ratio  of  pure-breeding  advances. 


INSTITUTIONAL  AND  PRUDENTIAL  SELECTION.  Ill 

We  may  also  assume  that  increased  segregate  fecundity  and  vigor 
will  make  the  multiplier  for  pure-breeds  =  2,  and  the  multiplier  for 
cross-breeds  =  ^.  And  when  another  ten  generations  have  passed, 
still  higher  degrees  of  segregation  will  be  the  natural  result. 

Conclusion. — We  have  now  approached  in  three  different  ways 
the  proof  of  cumulative  advance  in  a  set  of  innate  qualities,  which 
by  their  combined  action  produce  in  moderate  degress  both  positive 
and  negative  segregation.  The  result  seems  to  be  that  when  M 
by  any  chance  comes  to  be  larger  than  Mc  +  m,  then  the  fraction 

-=-= zr-f ,  which  gives  the  ratio  of  cross-breeds  to  pure-breeds,* 

M  —  Mc  —  m  ^  f  y 

becomes  a  positive  quantity,  and  a  given  proportion  of  the  whole 
stock  remains  unaffected  by  crossing.  This  point  having  been  reached 
the  subsequent  tendency  is  toward  a  constant  increase  in  the  segre- 
gative endowments. 

18.  Institutional  and  Prudential  Selection. 

Institutional  and  prudential  selection  stand  in  the  same  relation  to 
the  other  forms  of  reflexive  selection  that  artificial  selection  holds  in 
relation  to  natural  selection.  They  are  the  forms  of  reflexive  selec- 
tion established  in  communities  of  rational  beings  for  the  purpose  of 
securing  ends  that  are  more  or  less  fuUv  apprehended  as  the  goal. 

It  should  be  observed  that  inherited  instincts  have  an  important 
part  in  each  of  the  forms  of  conjunctional  selection,  that  is,  in  sexual, 
social,  and  filio- parental  selection;  and  again  in  the  forms  of  impreg- 
national  selection  and  impregnational  isolation  just  discussed,  the 
coordinations  are  due  to  inherited  characters,  either  morphological 
or  physiological ;  but  in  institutional  and  prudential  selection  the 
processes  are  guided  by  conscious  and  reflective  purpose.  It  will, 
therefore,  be  seen  that  the  conscious  regulation  of  relations  between 
husband  and  wife,  between  man  and  man,  or  between  parents  and 
children,  when  it  affects  the  form  of  survival,  belongs  to  either  insti- 
tutional or  prudential  selection,  and  not  to  conjunctional  select  ion 
in  any  one  of  its  three  forms.  In  the  past  history  of  man  the  three 
forms  of  conjunctional  selection  have  been  of  prime  importance ;  but 
as  civilization  advances  increasing  control  is  given  to  institutional  and 
prudential  selection.  Moreover,  in  the  case  of  civilized  man,  dominar 
tional  selection  through  intra-group  struggle  has  in  a  large  measure 
ceased  to  be  a  struggle  for  life  or  for  the  opportunity  to  have  a  full 
share  in  producing  the  next  generation,  and  has  become  chiefly  a 
struggle  for  influence  in  society  and  for  escape  from  certain  forms  of 


♦See  Formula  (4),  on  page  105. 


112  ANALYSIS  OF  THE  FOUR  PRINCIPLES. 

drudgery.  If  degeneracy  is  threatened,  the  remedy  will  not  be  found 
in  restoring  the  conditions  of  savage  life,  in  which  the  imbecile  and  the 
insane,  the  deaf  and  the  diseased,  are  all  eliminated  by  starvation ; 
but  rather  by  such  forms  of  institutional  and  prudential  selection, 
enforced  by  public  opinion  and  law,  as  will  prevent  the  marriage  of 
those  who  are  specially  liable  to  have  defective  offspring.  It  thus 
appears  that  institutional  selection  and  prudential  selection,  both  of 
which  may  be  subjected  to  rational  control,  are  the  chief  factors  by 
which  man  may  hope  to  maintain  and  control  his  own  evolution. 

The  powerful  influence  of  institutions  on  human  evolution  will  be 
recognized  by  those  who  consider  the  effects  that  must  be  produced 
on  the  vigor  and  vitality  of  a  nation  when  military  organization  and 
destructive  wars  prevent  many  of  the  most  vigorous  men  from  having 
any  share  in  producing  the  next  generation,  while  many  others  who 
leave  children  are  suddenly  removed  by  death  when  their  families 
most  need  their  aid.  Again,  the  institutions  in  which  the  commimity 
combines  for  the  maintenance  of  justice  and  order  and  the  training  of 
the  young  must  have  a  profound  influence  on  the  physical  inheritance 
of  the  race,  through  the  advantage  it  gives  to  the  peaceful  and  law- 
abiding. 

In  the  evolution  of  civilized  man  the  law  of  natural  increase  is 
liable  to  be  set  aside  in  a  way  that  often  becomes  extremely  abnormal. 
I  refer  to  the  effects  of  prudential  selection  in  limiting  the  size  of 
families,  both  by  delaying  marriage  and  by  restraint  after  marriage. 
Of  course,  both  methods  of  using  the  reason  are  legitimate  if  the  end 
sought  is  not  a  selfish  desire  to  be  free  from  care  and  responsibility. 
The  evil  has  grown  to  such  proportions  in  certain  communities  that 
the  very  existence  of  these  groups  is  thredtened.  The  fundamental 
difficulty  seems  to  be  that  public  opinion  has  failed  to  set  before  the 
men  and  women  of  force  and  character — before  those  who  are  the  back- 
bone of  the  nation— the  double  ideal  of  maintaining  a  vigorous  life 
and  civilization  during  their  own  generation  and  of  transmitting  the 
same  to  a  posterity  of  unabated  vigor  and  of  high  native  character, 
as  well  as  of  high  training  and  culture.  It  is  impossible  that  this 
standard  should  be  attained  if  there  is  unwillingness  to  establish 
family  relations  until  the  battle  of  life  has  been  fought  out  and  won. 
Nor  can  it  be  realized  if  after  marriage  those  who  should  become 
parents  wish  to  reserve  the  chief  portion  of  their  energy  for  social 
entertainments  or  for  the  pleasures  of  art,  science,  literature,  and 
travel,  with  no  consideration  of  how  these  great  gifts  of  past  genera- 
tions can  be  best  transmitted  and  rendered  continuously  progressive 


iNSTlTUtlONAL   AND  PRUDENTIAL  SELECTION.  II5 

in  the  hands  of  those  who  are  capable  of  receiving,  maintaining,  and 
transmitting  the  same.* 

This  factor  is  probably  having  a  profound  influence  on  the  present 
evolution  of  the  most  highly  civilized  nations.  In  his  volume  on  The 
Chances  of  Death,  Karl  Pearson  says  in  a  note  (see  p.  83) : 

Mr.  Francis  Galton  tells  me  that  he  was  recently  informed  by  credible  medical 
authorities  in  Paris  that  the  French  population  is  becoming  Breton,  owing  to  the 
fact  that  this  element  of  the  population  does  not  limit  its  fertility  to  anything  like 
the  same  extent  as  other  elements.  Nearly  all  large  families  are  found  to  be  of 
Breton  extraction. 

Similar  changes  of  population  are  taking  place  in  New  England  and 
in  other  countries,  and  in  some  of  these  cases  the  cause  is  probably  the 
one  we  are  now  considering.  The  continuance  of  any  human  race 
depends  not  only  on  its  power  to  produce  vigorous  and  adapted  off- 
spring in  sufficient  numbers,  but  on  its  willingness  to  exercise  this 
power  and  to  assume  the  heavy  responsibilities  of  rearing  and  train- 
ing the  young.  If  the  Bretons  are  willing,  and  persist  in  being  willing, 
France  may  become  their  inheritance;  if  they  give  way,  the  inheri- 
tance will  pass  to  others.  But  the  French  are  not  the  only  people 
that  are  threatened  by  this  selfish  individualistic  civilization.  Its 
blighting  effects  are  apparent  among  the  professional  and  commercial 
classes  in  other  countries.  The  statistics  obtained  by  Karl  Pearson, 
some  relating  to  families  of  Anglo-Saxon  extraction  and  others  relat- 
ing to  Danish  families,  do  not  give  the  proportion  of  the  same  classes 
that  remain  unmarried ;  but  careful  analysis  of  the  facts  given  leads 
him  to  remark : 

There  are  clear  traces  in  the  statistics  of  some  special  action  influencing  fertility 
in  families  with  between  3  and  7  children.  *  *  *  It  is  noteworthy  also  that 
this  characteristic  is  less  marked  in  statistics  drawn  from  pedigrees  than  in  more 
recent  natal  statistics.  I  can  not,  therefore,  avoid  the  conclusion  that  the  dip 
between  3  and  7  is  not  due  to  compoundness;  that  its  origin  is  comparatively 
recent,  and  that  it  is  an  artificial  break  in  the  natural  smoothness  of  the  curve  of 
fertility.  I  believe  it  to  be  entirely  due  to  a  Malthusian  restraint  on  population. 
Families  which  reach  7  and  over  appear  to  be  those  in  which  no  check  is  placed 
on  the  "natural"  growth.     Below  7  there  is  a  tendency  to  restraint  which  is 


*  Since  this  paragraph  was  written  Mr.  Francis  Galton  has  delivered  the  second 
Huxley  lecture  of  the  Anthropological  Institute  (of  London),  in  which  many 
suggestions  are  made  for  reversing  the  present  unfavorable  action  of  prudential 
selection.  The  lecture  is  entitled  "The  Possible  Improvement  of  the  Human 
Breed  under  the  Existing  Conditions  of  Law  and  Sentiment,"  and  is  published 
in  "Nature"  Oct.  31,  1901.  In  his  view  the  high  racial  development  of  the  most 
gifted  fiftieth  part  of  the  human  race  is  of  more  importance  than  the  suppression 
of  the  lowest  type,  though  he  recognizes  both  methods  as  needed  for  reaching  the 
best  results. 


114  ANALYSIS  OF  THE   FOUR  PRINCIPLES. 

marked  by  a  transference  of  frequency  from  families  which  should  lie  between  4 
and  7  to  those  lying  between  o  and  4.  *  *  *  While  the  theoretical  curve  will 
be  found  to  give  only  6  to  8  per  cent  of  marriages  without  issue,  we  find  in  modern 
statistics  1 1  to  18  per  cent  of  marriages  with  no  issue  *  *  *  ^^id  this  even 
in  countries  Uke  England  and  Denmark,  where  restraint  is  not  usually  supposed 
to  be  so  prevalent  as  in  France.* 

Again,  he  remarks:  "The  prudential  restraint  on  marriage  and 
parentage  in  the  more  educated  members  of  the  community,  which 
we  are  apt  to  regard  as  a  social  virtue,  may  after  all  have  its  dark 
side."t 

19.    Institutional  Election,  Partition,  and  Isolation. 

Institutional  election  arises  through  the  influence  of  public  opinion 
giving  prominence,  influence,  and  success  to  individuals  who  conform 
most  fully  to  the  social  standards  of  justice  and  propriety ;  and  is  rein- 
forced by  the  law  which  puts  a  definite  check  on  individuals  whose 
actions  fall  so  far  below  these  standards  that  the  community  will 
not  tolerate  the  offenders.  Again,  each  community  has  its  language, 
its  industrial  methods,  its  arts  and  sciences,  and  its  forms  of  etiquette, 
which  must  be  transmitted  by  tradition  from  generation  to  generation, 
for  these  attainments  can  not  be  transmitted  by  racial  heredity,  and 
their  continuance  in  the  community  depends  on  example,  education, 
and  training  on  the  part  of  the  older  generation,  and  on  the  part  of 
the  younger  generation  imitation,  study,  and  practice.  Now,  insti- 
tutional election  includes  the  superior  success  and  influence  of  the 
individuals  who  attain  the  most  complete  equipment  in  these 
acquired  characters  that  belong  to  the  community. 

Institutional  partition  arises  when  local  isolation  and  partition  has 
resulted  in  divergence  in  language,  religion,  and  education,  preventing 
the  possibility  of  association  in  one  community  when  local  isolation 
and  partition  has  ceased. 

Institutional  isolation. — Again,  the  differences  in  language,  religion, 
and  education,  which  prevent  free  association,  will  also  prevent  free 
intermingling  of  race,  and  the  result  is  institutional  isolation.  Exam- 
ples of  institutional  partition  and  isolation  are  seen  in  the  Mohamme- 
dan and  Christian  communities  occupying  the  same  regions  in  Turkey. 


*  See  Chances  of  Death  and  Other  Studies  in  Evolution,  pp.  67-69. 
■\Ibid.,p.  102. 


CHAPTER  VII. 


ANALYSIS  OF  THE  ^'OUR    PRINCIPLES   (CONTINUED). 

I.  The  Methods  of  the  Environai,  Mode  of  each  PrincipIvE,  with  the  Forms 

OK  EACH  Method. 


Producing  intensification  of  habitudinal 
groups: 
Environai  electipn, 
Endonomic  election. 
Habitudinal  election. 
Aptitudinal  election. 
Heteronomic  election. 
Natural  election. 
Artificial  election. 

Producing  intensification   of  racial 
groups : 
Environai  selection. 
Endonomic  selection. 
Habitudinal  selection. 
Aptitudinal  selection. 
Heteronomic  selection. 
Natural  selection. 
Artificial  selection. 


Producing  demarcation  of  habitudinal 
groups: 
Environai  partition. 
Endonomic  partition. 

Industrial  partition. 

Migrational  partition. 
Heteronomic  partition. 

Transportational  partition. 

Geological  partition. 

Artificial  partition. 

Producing  demarcation  of  racial 
groups: 
Environai  isolation. 
Endonomic  isolation. 
Industrial  isolation. 
Chronal  isolation. 
Seasonal  isolation. 
Cyclical  isolation. 
Migrational  isolation. ' 
Heteronomic  isolation. 
Transportational  isolation. 
Geological  isolation. 
Fertilizational  isolation. 
Artificial  isolation. 

Having  completed  our  analysis  of  the  methods  and  forms  of  the 
reflexive  mode  of  influence,  we  will  now  briefly  survey  the  forms  of  the 
environai  mode.  Under  each  or  the  four  principles,  when  we  find  that 
the  relations  between  the  group  and  its  environment  are  determined 
by  conditions  within  the  group,  we  call  the  influence  endonomic  selec- 
tion, election,  isolation,  or  partition,  as  the  case  may  be;  or  if  the 
relations  are  determined  chiefly  by  conditions  lying  outside  of  the 
group,  we  then  speak  of  the  influence  as  heteronomic. 

1.  Environai  Selection  and  Environai  Election. 
Environai  selection,  as  we  have  just  seen,  may  be  either  endonomic 
or  heteronomic. 

Divergent  forms  of  endonomic  selection  often  arise  through  divergent 
habittules  or  aptitudes  of  the  individuals  starting  the  isolated  colonies,  or 
through  the  cu:cidents  attending  the  entrance  of  small  groups  into  isolated 

i»5 


Il6  ANALYSIS    OF    THE    FOUR    PRiNCIPIvES  (CONTINUED). 

districts  presenting  the  same  environment. — In  my  paper  reproduced  in 
Appendix  II  of  this  volume  I  have  emphasized  the  fact  that  it  is  true 
of  a  very  wide  range  of  species  that  any  one  species  distributed  in 
small  sections  in  several  isolated  districts,  presenting  the  same  envi- 
ronment, will  often  use  the  environment  in  different  ways,  and  so  be 
subjected  to  different  forms  of  selection.  Selection  thus  determined 
by  the  relations  in  which  the  organism  puts  itself  to  the  environment 
I  call  endonomic  selection. 

We  shall  here  consider  in  fuller  detail  the  different  conditions  that 
may  produce  divergent  forms  of  selection  in  isolated  groups,  exposed  to 
the  same  environment.    Let  us  first  consider  cases  in  which  the  isolated 
groups  are  very  small,  and  from  a  species  with  many  variations  through 
adaptations  to  a  complex  environment,  and  in  which  the  new  dis- 
tricts to  which   they  are  brought  present  the  same  environment  as  is 
found  in  the  original  home  of  the  species.     That  the  conditions  may 
be  clearly  apprehended,  let  us  suppose  that  we  are  considering  a 
species  of  Hawaiian  tree-snails  on  the  southwest  side  of  the  main 
mountain  range  of  Oahu,  confined  to  the  shady  groves  of  a  single  val- 
ley, shut  in  on  either  side  and  at  the  head  of  the  valley  by  high  ridges 
covered  with  open  brush,  and  at  the  mouth  of  the  valley  by  grassy 
slopes  that  extend  to  the  sea.     This  snail  lives  continuously  on  the 
trees,  clinging  to  the  trunks  and  large  limbs  of  live  or  six  species,  and 
presents  many  variations  of  color  and  some  divergences  in  acquired 
habitudes  according  to  the  species  of  tree  on  which  it  has  lived.     If  for 
many  generations  a  certain  strain  should  live  entirely  on  one  species 
of  trees  (perhaps  occupying  a  single  grove  which  includes  no  other 
trees),  it  would  present  innate  aptitudes  for  that  kind  of  life,  devel- 
oped by  selection.     Now,  suppose  that  by  some  very  rare  accident  a 
man,  bearing  a  branch  of  a  tree,  unconsciously  transports  a  single 
impregnated  individual  of  this  species  of  snail  into  the  neighboring 
valley  on  one  side,  and  within  a  few  years  a  similar  occurrence  carries 
another  individual  of  the  same  species,  but  occupying  another  kind 
of  tree,  into  the  valley  on  the  other  side.     Each  individual  has  occu- 
pied but  one  kind  of  tree  for  its  whole  life,  and  having  formed  habi- 
tudes strongly  favoring  the  kind  it  has  so  far  used,  seeks  and  finds  the 
same  kind  in  the  new  district  to  which  it  has  been  brought.     As  there 
is  no  pressure  of  population  in  their  new  and  previously  unoccupied 
districts,  the  descendants  of  each  remain  for  a  hundred  years  or  more 
in  the  grove  in  which  the  first  comer  settled  down ;  and  the  two  colo- 
nies have,  perhaps  for  a  hundred  generations,  been  subjected  to  some- 
what divergent  forms  of  selection ;  for  the  habits  of  feeding  have  been 
different,  and  there  has  been  no  crossing  between  those  of  different 


ENDONOMIC   AND   HETERONOMIC   SELECTION.  II7 

habits,  as  was  the  case  in  the  original  home.  This  is  an  illustration 
of  what  I  call  "habitudinal  selection."  We  shall  next  consider  an 
illustration  of  aptitudinal  selection,  which  will  be  gained  by  changing 
the  illustration  just  given  at  one  point.  Instead  of  taking  the  two 
individuals  which  start  the  two  colonies  from  those  which  for  a  genera- 
tion have  been  feeding  on  different  kinds  of  trees,  we  must  take  them 
from  two  separate  strains  which  have,  for  many  generations,  had 
their  separate  methods  of  feeding,  so  that  not  only  their  habitudes 
but  their  aptitudes  must  be  somewhat  different.  Again,  we  may 
consider  conditions  that  would  produce  what  we  might  call  ''acci- 
dental selection."  This  might  occur  if  the  two  individuals  starting 
the  two  colonies  were  from  the  same  strain  and  had  both  of  them 
gained  various  experiences  by  feeding  on  different  trees,  so  that  their 
habits  were  not  fixed.  One  of  them  we  will  suppose  was  brought  by 
accident  to  a  fine  grove  of  candle-nut  trees  in  the  new  district,  and  for 
a  hundred  years  finds  no  cause  to  go  elsewhere;  while  the  other  one, 
in  another  valley,  is  brought  to  a  grove  of  what  the  Hawaiians  call 
ohia  trees,  and  there  remains  for  an  equal  number  of  years.  Is  it  not 
certain  that  the  selection  will  be  somewhat  divergent;  and  to  what 
determining  cause  shall  we  attribute  the  divergence  if  not  to  accidents 
that  started  these  individuals  of  varied  attainments  in  separate  colo- 
nies, and  in  groves  of  different  kinds  of  trees?  As  the  valleys  are 
near  together  and  on  the  same  side  of  the  mountain  range,  the  rain- 
fall and  other  features  of  climate  must  be  essentially  the  same.  If 
the  creatures  under  consideration  were  insects  endowed  with  higher 
powers  for  exploring  the  environment,  I  recognize  that  accidents  of 
the  kind  here  suggested  would  have  little  or  no  effect  in  determining 
the  forms  of  selection ;  for,  in  such  cases,  slight  differences  of  aptitudes 
or  habitudes  would  be  sure  to  control  the  method  of  using  the  environ- 
ment. Moreover,  such  species  would  not  fall  into  isolated  groups 
through  their  occupying  separate  valleys.  When  an  isolated  individ- 
ual or  pair  deals  with  an  environment  possessing  resources  that  are 
varied  but  familiar  and  easily  explored,  previous  habitudes  and  apti- 
tudes are  the  chief  factors  controlling  the  methods  of  using  the 
environment.  If  the  power  of  using  different  resources  is  great 
and  the  power  of  exploration  small,  the  method  of  using  the  envi- 
ronment may  be  determined  by  the  kind  of  resources  first  reached 
on  entering  the  district. 

Heteronomic  selection  is  of  two  forms — natural  selection,  produced  by 
conditions  in  the  environment  that  are  independent  of  any  purpose  to 
control  the  forms  of  survival,  and  artificial  selection,  which  is  deter- 
mined by  more  or  less  distinct  purpose  to  control  survival.     If  in  the 


Il8  ANALYSIS   OF  THE   POUR   PRINCIPLES    (CONTINUED). 

case  of  the  snails  just  considered  some  of  them  are  brought  to  groves 
on  the  northeast  side  of  the  mountain  range,  they  will  be  exposed  to  a 
somewhat  greater  rainfall,  and  will  probably  be  subjected  to  some 
change  through  the  resulting  selection.  Again,  suppose  a  colony  is 
planted  on  either  side  of  the  range,  in  a  valley  where  but  one  kind  of 
shade  trees  is  found,  and  this  a  kind  that  has  never  before  been  occu- 
pied by  the  species.  In  both  these  cases  we  should  have  heteronomic 
selection  of  the  form  that  has  been  called  natural  selection.  If  any 
of  these  snails  should  be  discovered  by  man  to  be  good  for  food  or 
medicine,  and  should  be  subjected  to  selection  for  the  purpose  of 
improving  the  qualities  sought,  the  result  would  be  heteronomic 
selection  of  the  artificial  form. 

Environal  election  corresponds  with  environal  selection  in  the 
general  influences  by  which  it  is  shaped ;  but  it  differs  in  the  results 
produced,  for  it  relates  to  the  intensifying  of  habitudes  and  acquired 
characters  within  the  associating  group.  The  higher  the  grade  of 
intelligence  the  more  marked  are  the  changes  and  divergences  intro- 
duced by  acquired  habitudes  and  characters,  and  accordingly,  in  such 
cases,  endonomic  election  becomes  the  leading  factor  by  which  some 
new  adjustment  to  the  environment  is  developed  into  an  established 
method  of  sustaining  life ;  and  if  the  inherited  endowments  are  not  in 
complete  accord  with  the  new  life,  coincident  selection  carries  the 
adjustment  to  higher  degrees;  for  variations  favoring  the  conditions 
imposed  by  the  new  tradition  will  have  the  advantage.  Examples  of 
endonomic  election  preceding  and  introducing  coincident  selection 
are  seen  in  the  tree-climbing  rats  mentioned  above,*  and  in  the  cats 
that  have  taken  to  wading  and  fishing,  f  Heteronomic  election  is 
either  natural  or  artificial.  Artificial  election  is  seen  in  dogs  and  other 
domestic  animals  that  have  been  subjected  to  training.  Natural 
election  is  seen  in  the  case  of  the  chimney  swift,  which,  in  a  large  meas- 
ure, having  lost  the  hollow  trees  in  which  it  used  to  build  its  nests, 
has  been  forced  to  find  a  substitute  in  the  chimneys  built  by  the 
intruders  who  cut  down  its  trees.  The  new  habit  is  undoubtedly 
being  reinforced  by  instincts  gradually  established  by  coincident 
natural  selection. 

2.   The  Methods  of  Environal  Isolation. 

Endonomic  isolation. — It  is  evident  that,  when  varieties  of  the  same 
species  of  plant  occupying  the  same  areas  are  prevented  from  crossing 
by  flowering  at  different  seasons,  the  process  which  I  call  seasonal 
isolation  is  rightly  classed  as  a  form  of  endonomic  isolation.     The 


*  See  page  loi.  f  See  pages  67-68. 


INDUSTRIAL   ISOLATION.  II 9 

same  is  true  of  the  cyclical  isolation  between  two  broods  of  the  period- 
ical cicada  when  occupying  the  same  district.*  As  each  brood  lives 
nearly  seventeen  years  burrowing  in  the  ground,  and  then  spends  the 
few  last  weeks  of  its  allotted  life  above  ground  breeding  in  the  trees,  it 
never  has  ^  chance  to  cross  with  the  other  brood,  whose  time  for  breed- 
ing comes  on  another  year,  and  each  seventeenth  year  thereafter.! 
Industrial  isolation  and  migrational  isolation,  so  far  as  they  are  deter- 
mined by  diversity  in  the  habits  or  instincts  of  the  members  of  the 
species,  must  also  be  classed  as  forms  of  endonomic  isolation. 

Heteronomic  isolation. — In  the  four  remaining  forms  of  environal 
isolation,  namely,  transportational,  geological,  fertilizational,  and 
artificial  isolation,  heteronomic  influences  must  prevail. 

3.  Industrial  Isolation. 

Industrial  isolation  is  isolation  arising  from  the  activities  by  which 
the  organism  protects  itself  against  adverse  influences  in  the  environ- 
ment, or  by  which  it  finds  and  appropriates  special  resources  in  the 
environment. 

The  different  forms  of  industrial  isolation  are  sustentational,  pro- 
tectional,  and  nidificational  isolation.  ^ 

For  the  production  of  industrial  isolation  it  is  necessary  that  there 
should  be,  in  the  same  environment,  a  diversity  of  fully  and  of  approx- 
imately available  resources  more  or  less  separated,  and  in  the  organ- 
ism some  diversity  of  adaptation  to  these  resources,  accompanied  by 
powers  of  search  and  of  discrimination,  by  which  it  is  able  to  find  the 
resources  for  which  it  is  best  fitted  and  to  adhere  to  the  same  when 
found. 

The  relation  in  which  these  causes  stand  to  each  other  and  through 
which  they  produce  segregation  may  be  described  as  separation 
according  to  endowment  produced  by  endeavor  according  to  endow- 
ment. From  the  nature  of  the  process  it  produces  segregation;  for 
those  of  like  aptitudes  are  brought  together. 

It  is  evident  that  if  initial  variation  presents  in  any  case  a  diversity 
of  adaptations  to  surrounding  resources  that  can  not  be  followed 
without  separating  those  differently  endowed,  we  shall  have,  in  the 
very  nature  of  such  variation,  a  cause  of  segregation  and  of  divergent 
evolution.  Some  slight  variation  in  the  digestive  powers  of  a  few 
individuals  makes  it  possible  for  them  to  live  exclusively  on  some  abun- 


♦For  a  full  statement  see  U.  S.  Department  of  Agriculture,  Division  of  Ento- 
mology, Bulletin  No.  8,  and  Bulletin  No.  14,  New  Series,  1898. 

t  For  a  comparatively  full  account  of  the  different  broods  of  this  species,  and 
the  problems  raised  by  the  remarkable  facts,  see  Appendix  II,  Sec.  Ill,  3. 


120  ANALYSIS   OF  THE   FOUR    PRINCIPLES    (CONTINUED). 

dant  form  of  food,  which  the  species  has  heretofore  only  occasionally 
tasted.  In  the  pressure  for  food  that  arises  in  a  crowded  community 
these  take  up  their  permanent  abode  where  the  new  form  of  food  is 
most  accessible,  and  thus  separate  themselves  from  the  original  form  of 
the  species.  These  similarly  endowed  individuals  will,  therefore,  breed 
together,  and  the  offspring  will,  according  to  the  law  of  divergence 
through  segregation,  be  still  better  adapted  to  the  new  form  of  food. 
When  other  forms  of  isolation  arise,  they  may  be  entirely  independent 
of  change  in  the  environment,  the  only  change  being  in  the  forms  or 
functions  of  the  organism. 

This  special  form  of  segregation  is  as  dependent  on  psychological 
causes  which  guide  the  organism  in  finding  and  in  adhering  to  the 
situation  for  which  it  is  best  fitted  as  it  is  on  the  initial  divergence  of 
the  more  strictly  physiological  adaptations  by  which  it  is  able  to 
appropriate  and  assimilate  the  peculiar  form  of  resource.  In  the  case 
of  freely  moving  animals  the  psychological  guidance  is  an  essential 
factor  in  the  success  of  the  individual,  while  in  the  case  of  plants  and 
low  types  of  animal  life  the  suitable  situation  is  reached  by  a  wide 
distribution  of  a  vast  number  of  seeds,  spores,  or  germs,  and  the  same 
situation  is  maintained  by  a  loss  of  migrational  power  as  soon  as  the 
germs  begin  to  develop.  In  these  lower  organisms  it  is  evident  that 
the  success  of  the  individual  must  depend  on  its  physiological  rather 
than  on  its  psychological  adaptations;  and  if  variation  results  in  a 
slight  difference  in  the  kinds  that  succeed  in  germinating  and  in  prop- 
agating in  contrasted  situations,  we  have  diversity  in  the  forms  of 
natural  selection  affecting  the  seed,  and  the  separation  is  what  I  here- 
after describe  as  local  isolation  passing  into  local  segregation.  We 
therefore  see  that  what  I  here  call  industrial  isolation  depends  on 
psychological  powers  acting  in  aid  of  divergent  physiological  adapta- 
tions to  the  environment,  or  in  aid  of  adaptations  that  are  put  to 
different  uses. 

Observation  shows  that  there  are  a  multitude  of  cases  in  which 
endeavor  according  to  endowment  brings  together  those  similarly 
endowed,  and  causes  them  to  breed  together ;  and  when  the  species  is 
thus  divided  into  two  or  more  groups  somewhat  differently  endowed, 
there  will  certainly  be  an  increased  divergence  in  the  offspring  of  the 
parents  thus  segregated ;  and  so  on  in  each  successive  generation,  as 
long  as  the  individuals  find  their  places  according  to  their  endowments, 
and  thus  propagate  with  those  similarly  endowed,  there  will  be  accu- 
mulated divergence  in  the  next  generation.  Indeed,  it  is  evident  that 
endeavor  according  to  endowment  may  produce  under  one  environ- 
ment what  natural  selection  produces  when  aided  by  local  separation 


INDUSTRIAL    ISOLATION.  121 

in  diflferent  environments.  As  it  produces  the  separate  breeding 
of  a  divergent  form  without  involving  the  destruction  of  contrasted 
forms,  it  is  often  the  direct  cause  of  divergent  transformations ;  while 
natural  selection  which  results  in  the  separate  breeding  of  the  fitted 
through  the  failure  of  the  unfitted  can  never  be  the  cause  of  divergence 
unless  there  are  concurrent  causes  that  produce  both  divergent  forms 
of  natural  selection  and  the  separate  breeding  of  the  different  kinds 
of  variations  thus  selected. 

Again,  endeavor,  according  to  endowment,  often  secures  separation 
according  to  endowment ;  and  this  gives  an  opportunity  for  the  inher- 
itable effects  of  diversity  of  endeavor  (if  there  are  such  effects),  to  be 
accumulated  in  successive  generations.  » 

In  the  relation  of  endowment  and  endeavor  we  have  a  striking 
example  of  the  peculiar  interdependence  of  vital  phenomena.  Diver- 
sity of  endowment  is  the  cause  of  diversity  of  endeavor  and  of  segre- 
gate breeding  according  to  endowment,  and  segregate  breeding  accord- 
ing to  endowment  is  the  cause  of  increased  diversity  of  endowment. 
It  is  very  similar  to  the  relation  between  power  and  exercise  in  the 
individual.  Without  power  there  can  be  no  exercise,  and  without 
exercise  there  can  be  no  continuance  or  growth  of  power. 

The  effects  of  industrial  isolation  are  specially  liable  to  be  enhanced 
by  that  form  of  intensive  segregation  which  I  have  suggested  should 
be  called  suetudinal  intension. 

Simple  and  familiar  as  the  principles  of  industrial  isolation  and  sue- 
tudinal intension  may  seem,  their  consistent  application  to  the  theory 
of  evolution  will  throw  new  light  on  a  wide  range  of  problems.  This 
law  of  divergent  evolution  through  industrial  segregation  rests  on 
facts  that  are  so  fully  acknowledged  by  all  parties  that  it  seems  to 
be  a  superfluous  work  to  gather  evidence  on  the  subject.  It  may, 
however,  be  profitable  to  consider  briefly  whether  the  cases  are  fre- 
quent in  which  different  habits  of  feeding,  of  defence,  or  of  nest- 
building  become  the  cause  of  separate  breeding  by  which  the  same 
habits  are  maintained  in  one  line  of  descent  without  serious  interrup- 
tion for  many  generations.  It  is  important  to  remember  (i)  that  the 
separate  breeding  will  arise  with  equal  certainty  whether  the  diversity 
in  the  habits  has  been  initiated  by  original  diversity  in  the  instincts 
and  adaptations  of  the  different  variations,  or  by  competitive  disrup- 
tion, through  the  crowding  of  population  inducing  special  efforts  to 
find  new  resources,  and  leading  to  diversity  of  endeavor;  and  (2)  that 
in  either  case  the  result  is  what  is  here  called  industrial  segregation. 
In  the  first  case,  when  the  creatures  are  guided  by  some  diversity 
of   inherited  instincts,  the  process  is  directly  segregative,  while  in 


122  ANALYSIS   OF   THE   I'OUR   PRINCIPLES    (CONTINUED). 

the  second  case  it  is  primarily  separative,  but  inevitably  passes  into 
segregate  breeding.  Divergence  through  diversity  of  use,  and  the 
resulting  diversity  of  acquired  characters,  whether  inherited  or  not, 
will  operate  as  surely  in  the  one  case  as  in  the  other. 

Sustentational  isolation  arises  from  the  use  of  different  methods  of 
obtaining  sustentation  by  members  of  the  same  species. 

There  can  be  no  doubt  that  of  the  innumerable  cases  where  phyto- 
phagic  varieties  (as  they  are  sometimes  called)  of  insects  exist,  a  con- 
siderable proportion  would  be  found  on  investigation  to  be  permanent 
varieties,  producing  offspring  that  are  better  adapted  to  the  use  of 
the  special  form  of  food  consumed  by  the  parents  than  are  offspring 
of  other  varieties ;  and  it  is  evident  that  if  the  peculiar  habits  of  each 
variety  had  no  tendency  to  produce  segregative  breeding  this  result 
would  not  be  reached,  for  each  variety  would  be  promiscuously  min- 
gled with  every  other,  and,  though  the  tendency  to  variation  might 
be  greatly  increased,  the  regular  production  of  any  one  variety  of 
young  would  be  prevented. 

Protectional  isolation  is  isolation  from  the  use  of  different  methods 
of  protection  against  adverse  influences  in  the  environment. 

When  a  new  enemy  enters  the  field  occupied  by  any  species, 
different  methods  of  escape  or  defence  are  often  open  to  the  mem- 
bers of  the  one  species ;  and  the  use  of  these  different  methods  must 
sometimes  result  in  segregating  the  members  according  to  the  methods 
adopted.  Some  may  hide  in  thickets  or  holes,  while  others  preserve 
themselves  by  flight.  Supposing  the  species  to  be  an  edible  butter- 
fly occupying  the  open  fields  and  the  new  enemy  to  be  an  insectivorous 
bird  also  keeping  to  the  open  country,  certain  members  might 
escape  by  taking  to  the  woodlands,  while  others  might  remain  in 
their  old  haunt,  gaining  through  protectional  selection  more  and 
more  likeness  to  some  inedible  species. 

Nidificational  isolation. — Let  us  now  consider  the  effects  of  diver- 
gent habits  in  regard  to  nest-building.  It  is  well  known  to  American 
ornithologists  that  the  cliff  swallow  of  the  eastern  portions  of  the 
United  States  has  for  the  most  part  ceased  to  build  nests  in  the  cliffs 
that  were  the  original  haunts  of  the  species,  and  has  availed  itself  of 
the  protection  from  the  weather  offered  by  the  eaves  of  civilized 
houses ;  and  that  with  this  change  in  nest-building  has  come  a  change 
in  some  of  its  other  habits.  Now,  there  is  reason  to  believe  that  if  the 
number  of  houses  had  been  limited  to  a  hundredth  part  of  those  now 
existing,  and  if  that  limited  number  had  been  very  slowly  supplied, 
this  gradual  change  in  some  of  the  elements  of  the  environment 
would  have  resulted  in  divergent  forms  of  adaptation  to  the  environ- 


CHRONAL  ISOLATION.  1 23 

ment  in  two  sections  of  the  same  species.  One  section  would  have 
retained  the  old  habit  of  building  in  the  cHffs,  with  all  the  old  adapta- 
tions to  the  circumstances  that  depend  on  that  habit,  while  another 
section  of  the  species  would  have  availed  itself  of  the  new  opportuni- 
ties for  shelter  under  the  eaves  of  houses,  and  would  have  changed 
inherited  adaptations  to  meet  the  new  habits  of  nest-building  and  of 
feeding.  It  is  also  evident  that  the  prevention  of  free  interbreeding 
between  the  different  sections  caused  by  the  diversity  of  habits  would 
have  been  an  essential  factor  in  the  divergence  of  character  in  the 
sections. 

It  simply  remains  to  consider  whether  the  industrial  habit  -that 
separates  an  individual  from  the  mass  of  the  species  will  necessarily 
leave  it  alone,  without  any  chance  of  finding  a  consort  that  may  join 
in  producing  a  new  intergenerant.  The  answer  is  that  there  is  no  such 
necessity.  Though  it  may  sometimes  happen  that  an  individual 
may  be  separated  from  all  companions  by  its  industrial  habit,  it  is 
usually  found  that  those  which  at  one  time  and  in  one  place  adopt  the 
habit  are  usually  sufficient  to  keep  up  the  new  strain  if  they  succeed 
in  securing  the  needed  sustenance. 

4.  Chronal  Isolation. 

Chronal  isolation  is  isolation  arising  from  the  relations  in  which  the 
organism  stands  to  times  and  seasons. 

I  distinguish  two  forms — -cyclical  and  seasonal  isolation. 

Cyclical  isolation  is  isolation  arising  from  the  fact  that  the  life-cycles 
of  the  different  sections  of  the  species  do  not  mature  in  ^he  same  years. 

A  fine  illustration  of  this  form  of  isolation  is  found  in  the  case  of 
Cicada  septendecim,  whose  habitat  is  the  northern  portion  of  the 
Mississippi  Valley  and  of  the  Atlantic  States,  though  many  outlying 
broods  are  found  in  other  regions.  The  typical  form  has  a  life-cycle 
of  seventeen  years,  but  there  is  a  thirteen-year  race  {Cicada  tredecim 
Riley)  found  chiefly  in  the  Southern  States,  and  therefore  separated 
from  the  typical  form,  both  locally  and  chronally.  As  the  life- 
cycle  of  this  race  is  thirteen  instead  of  seventeen  years,  in  a  district 
where  the  habitats  of  the  two  races  overlap,  even  if  there  were  no 
physiological  or  psychological  incompatibility  to  overcome,  inter- 
breeding could  occur  between  the  two  forms  only  once  in  221  years, 
that  is,  once  in  13  generations  of  the  longer-lived  race,  and  once  in 
1 7  generations  of  the  shorter-lived  race.  The  distribution  of  the  two 
races  in  different  districts  seems  to  indicate  that  local  isolation  under 
different  climatic  conditions  has  had  an  important  influence  in  their 
development.     It  is  manifest,  however,  that  if  during  a  period  of 


124  ANAI^YSIS  OF  THE   FOUR   PRINCIPLES    (CONTINUED). 

local  separation,  or  if  during  the  period  of  22 1  years  of  cyclical  separa- 
tion after  the  thirteen-year  race  was  first  formed,  this  race  should 
become  modified  in  the  season  of  its  appearing,  there  would  after  that 
be  no  mingling  of  race,  though  brought  together  in  the  same  districts. 
This  would  be  seasonal  isolation,  which  we  consider  in  a  following 
paragraph ;  but  what  is  of  special  interest  here  as  examples  of  com- 
plete cyclical  isolation  is  the  fact  that  in  each  of  several  limited  dis- 
tricts there  are  found  two  broods  of  the  same  race  whose  appearance 
above  ground  is  always  separated  by  the  same  number  of  years.* 

In  any  species  where  the  breeding  of  each  successive  generation  is 
separated  by  an  exact  measure  of  time  which  is  very  rigidly  regulated 
by  the  constitution  of  the  species,  cyclical  isolation  will  follow,  if, 
through  some  extraordinary  combination  of  circumstances,  members 
sufficient  to  propagate  the  species  are  either  hastened  or  delayed  in 
their  development,  and  thus  thrown  out  of  synchronal  compatibility 
with  the  rest  of  the  species.  If,  after  being  retarded  or  hastened  in 
development  so  that  part  of  a  cycle  is  lost  or  gained,  the  old  constitu- 
tional time  measure  reasserts  itself,  the  isolation  is  complete. 

In  such  cases,  so  far  as  the  time  of  maturing  is  concerned,  the  differ- 
ence is  segregative,  while  in  every  other  respect  it  will  be  simply 
separative,  except  as  separation  passes  into  segregation.  If  the 
periodical  cicada  was  as  variable  in  form  and  color  as  is  the  Achatinella 
(as  well  as  other  genera  of  Hawaiian  snails),  we  should  probably  find 
each  brood  characterized  by  easily  recognized  divergences. 

Seasonal  isolation  is  produced  whenever  the  season  for  reproduction 
in  any  section  of  the  species  is  such  that  it  can  not  interbreed  with 
other  sections  of  the  species.  It  needs  no  argument  to  show  that  if, 
in  a  plant  species  that  regularly  flowers  in  the  spring,  there  arises  a 
variety  that  regularly  flowers  in  the  autumn,  it  will  be  prevented  from 
interbreeding  with  the  typical  form.  The  question  of  chief  interest 
is,  under  what  circumstances  are  varieties  of  this  kind  likely  to  arise? 
Is  a  casual  sport  of  this  kind  likely  to  transmit  to  subsequent  genera- 
tions a  permanently  changed  constitution?  If  not,  how  is  the  new 
constitution  acquired?     One  obvious  answer  is  that  it  may  arise 

*  For  the  fullest  statement  yet  made  of  the  habitats  and  years  of  appearance 
of  the  14  broods  of  the  17-year  race  and  the  7  broods  of  the  13-year  race,  see 
Bulletin  14,  New  Series,  of  the  Division  of  Entomology,  U.  S.  Department  of  Agri- 
culture, 1898.  As  an  example  of  the  overlapping  of  the  habitats  of  two  broods 
of  the  same  race,  observe  that,  on  pp.  48  and  49  of  this  Bulletin,  three  of  the 
counties  of  Iowa  and  three  of  Missouri  are  given  as  part  of  the  district  where 
Brood  XIII  will  appear  in  the  year  191 2,  and  also  as  part  of  the  district  where 
Brood  XIV  will  appear  in  191 3,  both  broods  being  of  the  17-year  race.  Broods 
XXI  and  XXII,  of  the  17-year  race,  are  also  reported  as  appearing  a  year  apart 
in  Wilkes  County,  North  Carolina. 


CHRONAL  ISOLATION.  1 25 

under  some  special  influence  of  the  environment  upon  members  of  the 
species  that  are  geographically  or  locally  isolated  from  the  rest  of  the 
species. 

But  may  not  variation  in  the  flowering  season  of  a  fairly  homogen- 
eous species  tend  to  produce  greater  variation  in  that  respect  in  the 
next  generation,  and  so  on,  till  the  divergence  in  the  constitutional 
adaptation  to  season  is  carried  to  the  greatest  extreme  that  is  com- 
patible with  the  best  adaptation  to  the  environment?  I  believe  that 
it  not  only  may,  but  must  have  this  effect ;  and  that  the  result  will  be 
that  the  average  form  which  flowers  at  the  most  favorable  season  will 
so  vastly  predominate  over  the  extreme  forms  that  the  latter  will  be 
but  stragglers  in  comparison. 

In  regard  to  the  one  point  of  the  season  of  readiness  for  propagation, 
this  principle  is  segregative,  but  in  other  respects  it  is  simply  separa- 
tive, unless  through  the  principle  of  correlated  variation  other  charac- 
ters are  directly  connected  with  the  constitution  that  determines  the 
season.  It  will  be  observed  that  seasonal  isolation  is  produced  by  a 
parallel  and  simultaneous  change  in  the  constitution  of  members  in 
one  place  sufficient  to  propagate  the  species;  while  cyclical  segre- 
gation is  produced  by  a  simultaneous  acceleration  or  retardation  in 
the  development  of  members  in  one  place  sufficient  to  propagate  the 
species  without  disturbing  the  regular  action  of  the  constitution  under 
ordinary  circumstances. 

5.  Spatial  Isolation. 

Spatial  isolation  is  isolation  arising  from  the  relations  in  which  the 
organism  stands  to  space.  I  distinguish  two  forms,  viz,  geographical 
and  local  isolation. 

Geographical  isolation  is  isolation  that  arises  from  the  distribution  of 
the  species  in  districts  separated  by  geographical  barriers  that  prevent 
free  interbreeding.  Decided  differences  of  climate  in  neighboring 
districts  may  be  classed  as  geographical  barriers. 

Local  isolation  is  isolation  that  arises  when  a  species  with  small 
powers  of  migration  and  small  opportunities  for  transportation  has 
been,  in  time,  very  widely  distributed  over  an  area  that  is  not  sub- 
divided by  geographical  barriers.  The  segregation  in  this  case  is 
due  to  the  disproportion  between  the  size  of  the  area  occupied  and  the 
powers  of  communication  existing  between  the  members  of  the 
species  occupying  the  different  parts  of  the  area.  Though  it  is  often 
difficult  to  say  whether  a  given  case  of  isolation  should  be  classed  as 
geographical  or  local,  still  the  distinction  will  be  found  useful,  for  the 


126  ANALYSIS   O?  THE   FOUR   PRINCIPLES    (CONTINUED). 

results  will  differ  according  as  the  isolation  is  chiefly  due  to  barriers  or 
to  wide  diffusion  of  the  species.  In  geographical  isolation  the  result 
is  usually  the  development  of  well-defined  varieties  or  species  on  oppo- 
site sides  of  the  barriers;  but  in  local  segregation  it  often  happens 
that  the  forms  found  in  any  given  locality  are  connected  with  those 
in  surrounding  localities  by  individuals  presenting  every  shade  of 
intermediate  character,  and  in  general  terms  it  may  be  said  that  the 
forms  most  widely  separated  in  space  are  most  widely  divergent  in 
character.  It  is,  of  course,  apparent  that  when  the  divergence  has 
reached  a  certain  point  the  differentiated  forms  may  occupy  the  same 
districts  without  interbreeding,  for  they  will  be  kept  apart  by  some, 
if  not  all,  of  the  different  forms  of  autonomic  isolation. 

Three  different  forms  of  spatial  segregation  may  be  distinguished 
according  to  the  causes  by  which  they  are  produced,  viz : 

Migrational  isolation,  caused  by  powers  of  locomotion  in  the  or- 
ganism. 

Trans portaiional  isolation,  caused  by  activities  in  the  environment 
that  distribute  the  organism  in  different  districts.  Prominent  among 
these  are  currents  of  atmosphere  and  of  water,  and  the  action  of 
migratory  species  upon  those  that  can  simply  cling. 

Geological  isolation,  caused  by  geological  changes  dividing  the  ter- 
ritory occupied  by  a  species  into  two  or  more  sections.  For  example, 
geological  subsidence  may  divide  the  continuous  area  occupied  by  a 
species  into  several  islands,  separated  by  channels  which  the  creatures 
in  question  can  not  pass. 

Migration  differs  from  transportation  simply  in  that  the  former  is 
the  direct  result  of  activities  in  the  organism,  and  the  latter  of  activi- 
ties in  the  environment,  and  though  the  distribution  of  every  species 
depends  on  the  combined  action  of  both  classes  of  activities,  it  is 
usually  easy  to  determine  to  which  class  the  carrying  power  belongs. 
The  qualities  of  the  thistle-down  enable  it  to  float  in  the  air,  but  it  is 
the  wind  that  carries  it  afar. 

Some  degree  of  local  isolation  exists  whenever  the  members  of  a 
species  produced  in  a  given  area  are  more  likely  to  interbreed  with 
each  other  than  with  those  produced  in  surrounding  areas,  or  when- 
ever extraordinary  dispersal  plants  a  colony  beyond  the  range  of  ordi- 
nary dispersal — in  other  words,  when  those  produced  in  a  given  dis- 
trict are  more  nearly  related  with  each  other  than  with  those  produced 
in  surrounding  districts,  there  local  isolation  has  existed. 

There  is  one  important  respect  in  which  spatial  isolation  differs  from 
all  other  forms  of  isolation,  namely :  In  its  ordinary  operation  it  does 


SPATIAL   ISOLATION.  127 

not  bring  together  those  of  similar  endowments,  and  does  not  depend 
on  diversity.  The  dispersion  of  the  members  of  a  species  would  not  be 
prevented  if  each  was  exactly  like  every  other;  though,  of  course,  if 
there  were  no  power  of  variation,  separate  breeding  would  have  no 
influence  in  producing  divergence  of  character.  It  follows  that  every 
species  is  more  or  less  liable  to  be  affected  by  spatial  isolation; 
and  it  often  happens  that  other  forms  of  isolation  arise  through  the 
previous  operation  of  this  form;  but  as  spatial  isolation  prevents 
organisms  from  crossing  only  when  separated  in  space,  it  must  always 
be  reinforced  by  other  forms  of  isolation  before  well-defined  species 
are  produced  that  are  capable  of  occupying  the  same  district  without 
interbreeding.  Many  slightly  divergent  forms  arising  through  local 
isolation  are  reintegrated  with  the  surrounding  forms,  new  diverg- 
ences constantly  coming  in  to  take  the  place  of  the  old ;  but  if,  during 
its  period  of  local  divergence,  industrial  or  chronal  isolation  is  intro- 
duced, the  variety  becomes  more  and  more  differentiated,  and,  as  one 
after  another  the  different  forms  of  reflexive  segregation  arise,  it 
passes  into  a  well-defined  species. 

As  spatial  isolation  does  not  necessarily  depend  upon  diversity  in 
the  qualities  and  powers  of  the  organism,  it  usually  fails  of  distributing 
the  varieties  of  a  species  in  dififerent  localities  according  to  their 
differences  of  endowment.  The  causes  that  produce  it  are  primarily 
separative,  not  segregative. 

Migration  is  produced  by  the  natural  powers  of  the  organism  acting 
under  the  guidance  of  instincts  that  usually  lead  a  group  of  indi- 
viduals, capable  of  propagating  the  species,  to  migrate  together; 
while  organisms  most  dependent  on  activities  in  the  environment 
for  their  distribution  are  usually  distributed  in  the  form  of  seeds 
or  germs,  any  one  of  which  is  capable  of  developing  into  a  complete 
community. 

The  causes  of  isolation  between  the  different  sections  and  of  inte- 
gration between  the  members  of  one  section  are,  therefore,  sufficiently 
clear ;  but  what  are  the  causes  of  differences  of  character  in  different 
sections,  especially  when  they  are  exposed  to  the  same  environment? 
These  causes  all  come  under  what  I  call  typal  intensification  through 
diversity  of  success  and  diversity  of  survival. 


128  ANALYSIS   OF   THE    FOUR   PRINCIPLES    (CONTINUED). 

6.  Fertilizational  Isolation. 

Francis  Gallon's  short  article  on  "The  Origin  of  Varieties,"  which 
was  published  in  Nature,  vol.  xxxiv,  p.  395,  refers  to  this  cause  of 
isolation.     He  says: 

If  insects  visited  promiscuously  the  flowers  of  a  variety  and  those  of  the  parent 
stock,  then — supposing  the  organs  of  reproduction  and  the  period  of  flowering  to 
be  ahke  in  both,  and  that  hybrids  between  them  could  be  produced  by  artificial 
cross-fertilization — we  should  expect  to  find  hybrids  in  abundance  whenever 
members  of  the  variety  and  those  of  the  original  stock  occupied  the  same  or 
closely  contiguous  districts.  It  is  hard  to  account  for  our  not  doing  so,  except  on 
the  supposition  that  insects  feel  repugnance  to  visiting  the  plants  interchangeably. 

It  is  evident  that  isolation  of  this  form  depends  on  divergence  of 
character  already  clearly  established,  and,  therefore,  on  some  other 
form  of  isolation  that  has  preceded.  It  is  also  segregative  rather  than 
separative,  in  that  it  perpetuates  a  segregation  previously  produced,  * 
which  might  otherwise  be  obliterated  by  the  distribution  of  the  differ- 
ent forms  in  the  same  district.  The  form  of  isolation  that  precedes 
fertilizational  isolation,  producing  the  conditions  on  which  it  depends, 
must,  in  the  majority  of  cases,  be  local  isolation.  Chronal  and 
impregnational  isolation,  when  imperfectly  established,  might  be  for- 
tified by  fertilizational  isolation,  but,  in  the  case  of  plants,  these  are 
usually  dependent  on  previous  local  isolation. 

7.  Artificial  Isolation. 

Artificial  isolation  is  isolation  arising  from  the  relations  in  which 
the  organism  stands  to  the  rational  environment. 

The  importance  of  environal  isolation. — We  must  not  assume  that 
the  various  forms  of  environal  isolation  are  of  small  influence  in  the 
formation  of  species  because  sexual  or  impregnational  incompatibility 
is  a  more  essential  feature,  without  which  all  other  distinctions  are 
liable  to  be  swept  away.  The  importance  of  the  environal  forms  of 
isolation  lies  in  the  fact  that  they  often  open  the  way  for  the  entrance 
of  the  more  fundamental  forms  of  segregation,  even  if  they  are  not 
essential  conditions  for  the  development  of  the  same.  Though 
myriads  of  divergent  forms  produced  by  local  and  industrial  isolations 
are  swept  away  in  the  struggle  for  existence,  and  myriads  are  ab- 
sorbed in  the  vast  tides  of  crossing  and  intercrossing  currents  of  life, 
the  power  of  any  species  to  produce  more  and  more  highly  adapted 
variations,  and  to  segregate  them  in  groups  that  become  specially 
adapted  to  special  ends,  or  that  grow  into  specific  forms  of  beauty  and 
internal  harmony,  is  largely  dependent  on  these  factors. 


REGRESSIVE   MODES  OF  THE   PRINCIPLES.  1 29 

8.  Environal  Partition. 

Environal  partition  depends  on  influences  quite  similar  to  those 
producing  environal  isolation,  except  that  the  seasonal,  cyclical,  and 
f ertilizational  forms  are  wanting.  This  is  because  these  forms  depend 
on  inherited  characters  rather  than  on  acquired  habits,  while  envi- 
ronal partition  is  due  to  incompatibiUty  in  the  acquired  habits  of 
individuals  usually  belonging  to  groups  that  have  been  locally  sepa- 
rated for  a  time.  Industrial  and  migrational  partition  tend  more  or 
less  directly  to  produce  groups  with  somewhat  divergent  habits,  while 
transportational,  geological,  and  artificial  partition  open  the  way  for 
divergent  forms  of  innovation,  tradition,  and  election,  to  establish 
divergent  types  of  habitudinal  groups.  Moreover,  these  forms  of  par- 
tition tend  directly  to  produce  isolation  and  consequently  divergent 
racial  groups. 

II.  The  Regressive  Mode  of  Each  Segregative  Principle. 

Regressive  selection  may  be  produced  either  by  the  cessation  or  by 
the  reversal  of  a  long-established  form  of  selection.  Near  the  end 
of  the  last  chapter  we  referred  to  the  Old  World  cuckoo  and  the 
American  cow-bird  as  examples  of  degeneracy  in  the  instincts  for  nest- 
building,  for  incubation,  and  for  the  feeding  of  their  own  young — a 
degeneracy  that  seems  to  have  been  produced  by  the  gradual  cessa- 
tion of  the  selection  by  which  these  instincts  had  for  countless  gener- 
ations been  maintained.  We  also  found  that  there  was  reason  to 
beheve  that  the  discovery  of  substitutes  for  mother's  milk  is,  in 
certain  races  of  mankind,  leading  to  decay  of  the  power  to  give  suck, 
through  the  survival  of  the  children  of  mothers  who,  under  the  con- 
ditions of  primitive  times,  would  have  entirely  failed  of  having  any 
share  in  the  parentage  of  the  next  generation  of  parents.  Examples 
of  the  reversal  of  selection  are  found  in  the  history  of  species  that, 
through  the  coming  and  going  of  the  ice  age,  have  for  many  genera- 
tions been  subjected  to  increasing  cold,  and  then  for  many  generations 
to  increasing  warmth. 

Regressive  election  arises  when  any  tradition  or  acquired  character 
that  has  long  been  necessary  for  success  in  a  given  community  ceases 
to  be  so.  It  often  prepares  the  way  for  regressive  selection.  For 
certain  races  of  dogs  the  traditional  methods  of  finding  food  are  very 
different  from  those  that  were  current  with  their  primitive  ancestors, 
and  the  cessation  of  the  necessity  for  the  strenuous  life  of  the  old 
times  has  brought  regressive  selection,  resulting  in  the  decay  of  some 
of  the  old  instincts. 


t^6  AKfALVSIS  Of  tHE  iNduR  PRlI>fClPLES   (coNTINUEd). 

What  is  usually  called  the  amalgamation  of  races  is  regressive  isola- 
tion. It  is  a  form  of  racial  demarcation,  in  which  the  boundaries  are 
so  changed  that  two  or  more  slightly  divergent  varieties  or  races  are 
interfused  and  become  one.  But,  as  I  have  already  suggested,  the 
limits  within  which  regression  of  this  kind  can  take  place  are  compar- 
atively small. 

Regressive  partition  takes  place  when  divergent  forms  of  civiliza- 
tion become  commingled  and  blended.  In  the  case  of  human  races 
it  often  introduces  regressive  isolation. 

The  most  familiar  of  these  four  regressions  is  regressive  isolation, 
that  is,  racial  amalgamation,  to  which  Darwin's  work  on  cross  and  self 
fertilization  has  called  attention.  The  chief  significance  of  the  prin- 
ciple lies  in  its  producing  a  certain  limited  undoing  of  isolation  and  in 
its  giving  plasticity  and  variability  to  the  compounded  stock.  Amal- 
gamation usually  arises  through  the  entrance  of  divergent  races  into 
the  same  region  before  their  sexual  and  social  instincts  or  the  physio- 
logical and  structural  coadaptations  of  the  sexes  have  become  so 
divergent  as  to  prevent  interfusion.  Under  such  conditions  what- 
ever determines  the  bringing  together  of  the  races  in  the  same  region 
determines  the  nature  of  the  amalgamation.  When  human  races  are 
brought  together  in  the  same  region,  the  rapidity  of  amalgamation  is 
determined  largely  by  racial  instincts  and  social  conditions. 

1 .  Reversal  of  Partition  and  Isolation  in  Man. 

The  most  remarkable  feature  in  the  evolution  of  civilized  man  is  the 
reversal  of  the  processes  of  partition  and  of  isolation  and  the  breaking 
down  of  the  social  and  racial  segregations  that  have  been  progressing 
for  countless  generations.  The  leading  factors  in  this  process  of 
coalition  are  social  rather  than  racial;  but  the  final  result  will  un- 
doubtedly be  a  great  reduction  of  the  number  of  races,  and  possibly  a 
blending  of  all  in  one  generalized  type,  resulting  from  the  amalgama- 
tion of  all  the  races  in  one.  It  is,  however,  possible  that  the  barriers 
preventing  marriage  between  certain  races  of  men  will  become  more 
fixed  than  ever,  even  though  the  intercourse  of  industrial,  commercial, 
and  national  life  becomes  increasingly  intimate.  The  era  of  commer- 
cial intercourse  has  been  inaugurated  and  will  never  be  reversed. 
Again,  the  smaller  nations  are  being  absorbed  into  the  larger  nations ; 
but  what  the  final  result  will  be  on  the  multitude  of  races  and  castes 
can  not  be  easily  foretold. 


NO  REFLEXIVE  SELECTION  BETWEEN  GROUPS.  131 

2    Isolation  Prevents  Reflexive  Selection  between  Grcups. 

We  are  now  prepared  to  understand  one  reason  why  isolation  result- 
ing from  indiscriminate  separation  is  in  time  transformed  into  segre- 
gation. Isolation  is  in  its  very  nature  the  suspension,  not  only  of  one 
form,  hut  of  all  forms  of  reflexive  selection  between  the  separated  portions 
of  the  species.  The  importance  of  the  cessation  of  natural  selection 
in  producing  the  different  stages  of  the  degeneration  of  organs  that 
have  ceased  to  be  of  use  has  been  fully  discussed  by  Romanes  (see 
Nature,  Vol.  41,  p.  437,  and  previous  communications  there  referred 
to),  who  points  out  that,  as  the  power  of  the  special  form  of  heredity 
by  which  any  organ  has  been  produced  has  been  built  up  by  many 
generations  of  natural  selection  that  have  acted  in  favor  of  the  organ, 
so  the  gradual  weakening  of  that  power  follows  the  cessation  of 
the  natural  selection.  Professor  Weismann  seems  to  appeal  to  the 
same  principle  when  he  attributes  the  reduced  size  of  "rudimentary 
organs"  to  the  action  of  "panmixia."  Now,  since  isolation  always 
includes  the  complete  cessation  of  reflexive  selection  between  the 
separate  groups,  a  similar  principle  is  introduced,  and  the  result  must 
be  the  weakening  of  the  power  of  heredity  by  which  the  portions  of  the 
species  were  held  in  correspondence  with  each  other  before  their  sepa- 
ration. I  have  elsewhere  shown  that  isolation  necessarily  disturbs 
unstable  adjustments;  and  we  here  see  that  the  most  stable  of  the 
adjustments  by  which  each  part  of  a  species  is  kept  in  correspondence 
with  every  other  part  gradually  becomes  unstable,  under  the  con- 
tinued influence  of  isolation.  Whenever  a  species  is  divided  into  two 
portions  that  do  not  interbreed,  the  forms  of  reflexive  selection  above 
described  will  cease  to  act  between  the  two  portions,  and  they  will 
continue  in  sexual,  social,  physiological,  and  industrial  harmony  with 
each  other  only  in  so  far  as  the  force  of  the  old  heredity  holds  them  to 
the  old  standards.  But  the  force  of  heredity  in  these  respects  will  in 
time  fail  if  the  reflexive  selection  that  held  the  original  stock  in  accord 
is  entirely  removed  in  its  action  between  the  two  portions.  If  the 
separate  breeding  is  long  continued,  incompatibility  in  all  these  re- 
spects tends  gradually  to  arise ;  but  it  is  manifest  that  incompatibility 
of  industrial  habits  implies  diversity  in  the  forms  of  environal  selec- 
tion shaping  each  portion.  I  therefore  maintain  that  separation, 
which  necessarily  includes  the  cessation  of  reflexive  selection  between 
the  portions  separated,  is  a  cause  of  segregation  and  divergence  and 
that  it  introduces  diversity  of  environal  selection,  which  is  a  still 
further  cause  of  divergence. 


132  ANAtVSIS  OP  THE    FOUR    PRINCIPLES   (CONTINUED). 

III.  Discriminate  and  Indiscriminate  Action  of  the  Segregative 

Principles.* 

1.  Discriminate  Action. 

Under  each  of  these  four  segregative  principles  we  may  raise  the 
question  as  to  the  difference  in  the  results ;  first,  when  the  principle 
under  consideration  is  guided  by  some  discriminative  influence, 
continued  from  generation  to  generation,  and,  second,  when  it  acts 
without  discrimination  and  without  cumulative  results  in  successive 
generations.  It  is  evident  that  discriminative  survival,  which  is  the 
same  as  selection,  when  continued  in  the  same  form  for  successive 
generations,  must  be  cumulative  in  its  effects.  Discriminative  iso- 
lation, that  is,  segregate  intergeneration,  arises  whenever  adapta- 
tion for  appropriating  certain  resources  brings  together  in  one  iso- 
lated group  those  that  are  by  innate  qualities  and  aptitudes  the 
better  adapted.  In  most  of  these  cases  it  is  not  possible  that  another 
group  should  arise  within  this  first  group  simply  through  being  more 
highly  endowed  in  the  same  respect.  Cumulative  isolation  is  for  the 
most  part  produced  by  the  subdivision  of  groups  that  have  already 
been  established,  and  the  agencies  producing  the  successive  divisions 
are  likely  to  be  different  in  their  nature;  and,  therefore,  not  cumu- 
lative in  their  effects  upon  any  one  character.  This,  however,  does 
not  prevent  each  isolation  from  being  more  or  less  segregative  in 
regard  to  some  of  the  characters. 

Election,  that  is,  the  discriminate  success  of  individuals  through  the 
attainment  of  certain  habitudes  and  acquired  characters,  is  likely  to 
be  cumulative  in  the  effects  produced  on  successive  generations;  for, 
as  long  as  increased  facility  in  the  performance  of  certain  acts  is  an 
advantage,  both  habitudes  and  aptitudes' aiding  in  the  performance 
will  be  combined  in  an  increasing  degree  in  each  generation. 

Discriminate  partition,  that  is,  segregate  association,  arises  when- 
ever adaptation  for  dealing  with  either  the  environment  or  the  social 
conditions  brings  together  in  one  separate  group  those  that  are  by 
habitudes  (that  is,  by  acquired  characters),  the  best  adapted.  It  is 
manifest  that  among  social  organizations  occasions  producing  such 
partition  must  often  arise;  and  it  seems  probable  that  among  even 
the  least-endowed  creatures  great  advantage  must  sometimes  come  to 
those  who  have  in  some  degree  acquired  characters  enabling  them  to 
meet  new  conditions  in  the  environment,  which  come  upon  the  spe- 
cies with  a  sweep  that  none  who  are  unprepared  can  withstand.     Such 


♦See  Table  of  "Discriminate  and  Indiscriminate  Forms,"  page  136. 


INDISCRIMINATE   ACTION  OF  THE   PRiNCIPIvES.  1 33 

changes  are  sometimes  experienced  in  temperature ;  or  in  the  salinity 
of  the  water,  in  the  case  of  water  plants  and  animals. 

2.  Indiscriminate  Action  of  the  Segregative  Principles. 

Again,  let  us  consider  what  the  results  are  when  the  action  of  these 
principles  is  indiscriminate.  Indiscriminate  survival  takes  place  in 
regard  to  any  given  character  of  a  species  when  the  presence  or  absence 
of  the  character  has  no  effect  on  the  adaptation  of  the  individual.  For 
Anglo-Saxons  the  possession  of  blue  eyes  or  gray  eyes  is  a  matter  of 
non-selective  importance,  and  selection  does  not  determine  which  shall 
prevail.  There  is,  however,  another  form  of  indiscriminate  survival 
which  may  have  definite  influence  in  determining  the  subsequent  form 
of  a  race  or  species.  I  refer  to  the  indiscriminate  destruction  of  all  but 
a  small  portion  of  the  intergenerating  group.  Against  heavy  volcanic 
convulsions  the  varying  endowments  of  different  individuals  of  any 
one  species  usually  count  for  nothing,  and  therefore  the  destruction 
falling  upon  them  is  indiscriminate ;  but  if  only  a  pair  or  two  are  left  to 
propagate  the  species,  the  probability  is  that  the  type  will  be  more  or 
less  changed  in  one  or  more  of  its  characters. 

Indiscriminate  isolation  of  only  a  small  fragment  of  a  species  is  liable 
to  result  in  important  divergence  in  one  or  more  of  the  characters  of 
the  species.  If  a  single  gravid  individual,  of  a  variable  species  of 
Hawaiian  tree  snails,  is  carried  for  a  mile  or  two  from  its  native  val- 
ley while  clinging  to  a  leaf  borne  by  a  bird  or  a  strong  wind,  it  may 
fall  in  a  neighboring  valley,  among  groves  and  thickets  of  the  same 
trees  and  shrubs  that  furnished  its  natural  station  in  its  original 
home.  Is  there  now  any  probability  that  the  colony  descending 
from  this  individual,  completely  isolated  from  the  original  stock,  but 
living  in  a  valley  with  the  same  climate,  and  vegetation,  and  birds, 
and  insects  as  are  found  surrounding  their  relatives  in  the  original 
valley,  will,  by  any  chance,  reproduce  all  the  variations  and  varie- 
ties of  the  original  species,  and  in  the  same  proportions,  and  at  the 
same  time  avoid  producing  any  new  varieties?  My  knowlege  of  var- 
iable animals  in  general,  and  my  observations  on  Hawaiian  snails  in 
particular,  make  it  impossible  for  me  to  beheve  that  such  a  case  could 
ever  occur.  If  anyone  says  that  an  isolated  portion  of  a  species  under 
absolutely  the  same  environment  as  the  original  stock  must  produce  the 
same  varieties,  as  Wallace  maintains  in  his  volume  entitled  ' '  Darwin- 
ism," I  suspect  he  is  using  the  word  "  environment  "  as  equivalent  for 
all  the  conditions  that  may  cause  divergence,  whether  they  lie  within 
the  species  or  belong  to  what  lies  outside  of  the  species.  This  seems  to 
be  in  part  the  explanation  of  Wallace's  position ;  for  in  enumerating  the 


134  ANAtYSiS   OF   THE   I^OUR  PRINCIPLES    (cONtlNUED). 

conditions  in  the  environment  that  may  have  an  effect  in  producing 
divergence,  he  calls  attention  to  the  fact  that  the  small  isolated  por- 
tion of  the  species  "is  at  once  in  a  different  position  as  regards  its 
own  kind."  Now,  this  is  exactly  what  I  mean  when  I  say  that  the  iso- 
lation of  a  small  portion  has  some  effect  in  producing  divergence,  even 
if  the  conditions  outside  of  the  species  could  be  absolutely  the  same 
as  in  the  original  habitat.  Still  further,  as  I  have  abundantly  shown 
in  the  paper  reproduced  in  Appendix  II,  it  is  very  possible  that  the 
isolated  portion  will,  early  in  its  career,  if  not  from  the  very  first,  be 
subjected  to  new  forms  of  selection,  through  the  adoption  of  habits 
of  feeding  that  are  wanting,  or  unusual,  in  the  original  habitat ;  for  a 
rare  habit  in  the  original  valley  might  become  the  predominant  habit 
in  the  colony  that  arises  in  the  newly  occupied  valley,  even  if  the  envi- 
ronments were  absolutely  the  same.  This  form  of  selection  I  have 
called  active  (or  endonomic)  selection. 

Indiscriminate  success  will  arise  in  regard  to  any  given  habitude, 
or  form  of  acquired  efficiency,  when  the  attainment  or  the  non-attain- 
ment of  the  habitude  has  no  effect  on  the  success  or  influence  of  the 
individual.  Another  form  of  indiscriminate  influence  may  be  intro- 
duced by  the  indiscriminate  slaughter  of  all  but  a  few  individuals 
of  a  community,  in  which  case  the  habits  of  the  few  remaining  indi- 
viduals will  have  great  influence  on  the  habits  of  the  new  community 
arising  through  the  multiplication  of  the  few  survivors. 

Indiscriminate  partition  arises  whenever  the  occasion  that  brings  a 
number  of  individuals  of  a  species  together  in  a  sepafate  position  does 
not  determine  that  they  shall  be  of  any  particular  type  of  habitudes, 
of  culture,  or  acquired  skill.  Partition  due  to  an  island  being  divided 
by  partial  submergence  is  usually  indiscriminate;  while  migration 
often  produces  discriminate  partition,  as  when  it  brings  to  a  distant 
island  men  who  are  skilled  in  canoe  building  and  sailing. 

3.  Contrasts  in  Discriminate  and  Indiscriminate  Forms  of  Action. 

These  considerations  bring  to  light  the  following  facts : 
( I )  In  the  survival  of  innate  characters  and  the  success  of  acquired 
characters  the  discriminate  forms  (i.  e.,  selection  and  election)  are 
of  prime  importance ;  for  in  one  way  or  another  they  are  continually 
acting  on  nearly  every  generation  of  nearly  every  species.  The  cases 
must  be  rare  in  which  equal  success  and  survival  are  attained  by 
all  the  variations ;  for  if  variations  in  other  respects  have  no  effect, 
its  variations  in  vigor  will  have  relation  to  the  degree  of  survival. 
In  some  rare  cases  there  will  occur  the  indiscriminate  elimination  of 
all  but  a  very  few  members  of  a  race  or  species;  and  the  results 


DISCRIMINATE   AND  INDISCRIMINATE   ACTION.  135 

in  such  cases  are  liable  to  be  of  importance,  through  the  original 
average  character  of  the  species  not  being  fully  represented  and 
through  the  fact  that  this  initial  bias  often  leads  to  some  new 
form  of  selection,  which  continues  to  act  with  cumulative  force 
through  subsequent  generations.  No  single  pair  can  exactly  repro- 
duce the  average  character  of  the  species  in  all  its  aptitudes 
and  habitudes,  and  therefore  the  methods  of  dealing  with  the  environ- 
ment adopted  by  the  descendants  are  liable  to  be  different. 

(2)  In  isolation  and  partition  there  is  less  opportunity  than  in 
selection  and  election  for  cumulative  effects  in  each  generation. 
Moreover,  in  many  of  the  cases,  the  isolation  is  indiscriminate  till 
divergent  forms  of  selection  cooperate.  But  it  should  be  noted  that 
the  isolation  of  a  small  number  of  the  species  is  of  frequent  occurrence, 
and  the  failure  of  these  small  groups  to  represent  the  average  charac- 
ter of  the  group  or  race  either  in  habitudes  or  aptitudes  introduces 
slight  divergences  determining  new  forms  of  autonomic  selection 
which  are  of  great  importance  in  molding  new  types.  And  even 
when  large  masses  are  indiscriminately  isolated  all  selection  pro- 
ducing coordinations  between  the  members  of  the  separate  groups 
ceases ;  and  the  probability  is  that  in  the  course  of  many  generations 
divergent  forms  of  selection  will  arise,  through  different  methods  of 
coordination  between  members  as  well  as  through  dififerent  methods  of 
dealing  with  the  environment  adopted  by  different  isolated  groups. 
This  probability  rests  not  so  much  on  the  probability  of  a  difference 
in  the  average  character  of  the  two  large  sections  as  on  the  probability 
that  in  one  section  some  new  habitude  will  arise  that  does  not  arise  in 
the  other  section.  The  importance  of  isolation  in  producing  diver- 
gence is  seen  not  only  in  its  being  the  absolute  condition  on  which 
divergent  forms  of  selection  become  of  avail  in  producing  divergence, 
but  in  the  fact  that  the  isolation  of  a  few  individuals  often  introduces 
from  the  first  a  divergent  form  of  autonomic  selection,  though  the 
environment  is  the  same,  and  in  the  fact  that  the  isolation  of  a  large 
section  of  a  species  opens  the  way  for  a  similar  divergence  of  selection, 
though  it  may  require  many  generations  for  the  result  to  become 
apparent.  Moreover,  discriminate  isolation  (as  when  different  indus- 
tries have  led  individuals  to  form  intergenerating  groups  according  to 
their  aptitudes),  leads  from  the  first  to  divergence  in  adaptations  and 
to  the  intensification  of  adaptations. 

The  table  on  page  136  will  be  useful  in  enabling  us  to  keep  in  mind 
the  importance  of  these  distinctions  when  applied  to  some  of  these  prin- 
ciples. Discriminate  survival,  which  is  usually  called  selection,  is  of 
such  importance  that  many  terms  have  been  needed  to  present  the 


136  ANALYSIS   OF   the;   FOUR    PRINCIPLES    (CONTINUED). 

different  influences  through  which  it  arises;  while  indiscriminate 
survival  and  its  equivalent,  indiscriminate  elimination,  seem  to  be 
sufficient  for  the  designation  of  a  process  which,  as  compared  with 
selection,  is  rarely  effective  in  producing  the  transformation  of  races. 

4.   Table  of  the  discriminate  and  indiscriminate  forms  0}  the  four  segregative 

principles. 


The   Eight  Forms. 


Partition. 


1.  Discriminate   partition  —   segregate    asso- 
ciation. 


2.  Indiscriminate  partition  with  more  or  less 

loss  of  power  to  perpetuate  the  original 
habitudes  unchanged. 

Success. 

3.  Discriminate  success  —  election. 


4.  Indiscriminate   success    —     indiscriminate 

failure. 

Isolation. 

5.  Discriminate  isolation   —    segregate  inter- 

generation. 


6.  Indiscriminate  isolation  with  more  or  less 

loss  of  power  to  reproduce  the  complete 
average  of  the  innate  characters  ot  the  orig- 
inal stock. 

Survival. 

7.  Discriminate  survival  —  selection. 


8.  Indiscriminate  survival    —    indiscriminate 
elimination. 


The   Results. 


1 .  Grouping  of  individuals  according  to  habi- 

tudes and  acquired  characters,  and  so 
producing  liabitudinal  segregation,  and 
giving  an  initial  tendency  toward  segre- 
gate breeding. 

2.  More  or  less  divergence  in  the  habitudes 

and  acquired  characters  of  the  separated 
groups,  especially  when  the  groups  are 
very  small,  and  so  producing  initial  babi- 
tudinal  segregation. 

3.  Success  and  influence  of  individuals  accord- 

ing to  their  acquired  fitness  for  the  condi- 
tions, both  social  and  physical,  in  which 
they  are  placed,  producing  intensified 
habitudinal  segregation. 

4.  When  the  number  of  individuals  that  es- 

cape from  a  sweeping  catastrophe  is  very 
small,  they  will  be  unable  to  perpetuate 
the  original  social  organization  unchanged. 

5.  Grouping  of  individuals  according  to  their 

aptitudes  and  innate  characters,  and  so 
directly  introducing  segregate  breeding 
with  divergence  of  characters,  i.  «.,  racial 
segregation. 

6.  More  or  less  divergence  in  the  aptitudes 

and  innate  characters  of  the  isolated 
groups,  especially  when  at  the  time  of  the 
first  setting  apart  the  group  is  represented 
by  but  one,  or  but  few,  individuals,  and 
so  producing  initial  racial  segregation. 

7.  The  efficiency  of  individuals  in  living  and 

propagating  will  vary  (and  so  their  survi- 
val will  vary)  according  to  their  innate 
fitness  for  the  struggle  of  life,  and  thus 
the  fitness  of  the  race  will  be  increased. 

8.  When  those  indiscriminately  surviving  are 

very  few,  it  will  be  impossible  for  them  to 
reproduce  all  the  innate  characters  of  the 
original  stock  unchanged. 


CHAPTER  VIII. 

CLASSIFICATION    OF   THE   FORMS    OF    THE    PRINCIPLES 
PRODUCING  ALLOGAMIC  EVOLUTION. 

I.  Tables  of  Forms,  with  Brief  Explanations 

The  analysis  presented  in  the  two  preceding  chapters  has  revealed 
many  factors,  which  are  here  brought  together  in  tables  so  arranged 
as  to  show  the  more  important  of  their  relations  to  each  other.  (See 
pages  138-139.) 

1.  Allogamic,  Autogamic,  and  Agamic  Evolution. 

A  complete  classification  of  the  factors  of  organic  evolution  must 
include  the  principles  producing  differentiation  of  organisms  multi- 
plying asexually,  as  well  as  of  those  reproducing  sexually.  Moreover, 
the  reproduction  of  self-fertilizing  species  is  so  unlike  that  of  species  in 
which  cross-fertilization  takes  place  (either  in  each  generation  or  at 
the  end  of  a  series  of  generations),  that  it  seems  necessary  to  consider 
their  methods  of  transformation  separately.  Following  these  dis- 
tinctions, organic  evolution  needs  to  be  divided  into  three  depart- 
ments, which  may  be  called : 

Allogamic  evolution,  which  relates  to  the  evolution  of  cross-fertiliz- 
ing organisms ; 

Autogamic  evolution,*  which  relates  to  the  evolution  of  self -fertil- 
izing organisms ;  and 

Agamic  evolution,  which  relates  to  the  evolution  of  organisms 
whose  reproduction  is  continuously  asexual. 

The  investigation  presented  in  this  volume  relates  to  allogamic 
evolution. 


*  Karl  Pearson,  in  2nd  ed.  of  "The  Grammar  of  Science,"  London,  1900,  p.  423, 
uses  the  term  "Autogamic  Mating"  to  designate  self-fertilization. 

»37 


138 


CLASSIFICATION  OP  THE  FORMS   OF   THE  PRINCIPLES. 


2.  AUogamic  Evolution  Controlled  by  the  Four  Principles  of  Segregation. 


+_&^  = 

C.     Typal  demarcation  '.•  autonomic  demar-    i 

D. 

Typal  intensification  "."  autonomic  intensifica- 

.C  -5  S 

cation  --  I  +  II,  and  '."  heteronomic  demar- 

tion =    III   -i-  IV.  and   ".'  heteronomic  intensifi- 

11 III 

cation  =  V  +  VI. 

1 

cation  -  VII  -i-  VIII. 

(E")   Habitudinal  demarcation,  through  par-   | 

(G)   Habitudinal    intensification  through  success 

tition. 

(through  election  when  discriminate).                | 

5   'J   be T* 

f  o.   Reflexive  partition. 

0-   Reflexive  election.                                 "| 

i.i-.li  = 

1           1.  Conjunctional  partition. 

10.  Conjunctional  election. 

i>  fc  =  E 

(1)   Family  partition. 

(29)  Sexual  election. 

^ 

.o  +  l-sS 

(2)  Social  partition. 

*> 

c 

(30)   Social  election. 

^ 

'i>^i  = 

2.   Institutional  partition. 

? 

(31)   Filio-parental  election. 

> 

i"-3i5 

■ 

(3)   Linguistic  partition. 

§ 

11.   Dominational  election. 

B 

c-s  >  =  c 

1 

(4)  Religious  partition. 

(5)  Educational  partition 

n 

12.   Institutional  election. 
(32)   Religious  election. 

0 

a 
0 

3 

:-|ll'= 

U 

(6)  Sanitary  partition. 

1 

*c# 

(33)   Educational  election. 

0' 

C  S "  trS 

^  -! 

*: 

(34)  Sanitarj-  election. 

r5_ 

tag's  sic 

■*-• 

6.   Environal  partition. 

0" 

s 

(35)   Penal  election. 

JT 

Sog-ss 

•o 

3.  Endonomic  partition. 

a 

■0 

h.  En^^^onal  election. 

3' 

£■§:§§& 

1 

(7)  Industrial  partition. 

B 

13.   Endonomic  election. 

8^8-3 

(8)   Migrational  partition. 

0 

f36)   Habitudinal  election.             ' 

-  £  S'S-S 

4.   Heteronomic  partition. 

§< 

(37)  Aptitudinal  election.             J 

CS  «-2  3 

(9)  Transportational  par- 

3 

"3*  V  «-s 

tition,  a; 

■s-S= 

14.   Heteronomic  election,     -i       VII.  Hete- 

(38)  Xatural  election.        Y        ronomic 

(39)  Artificial  election.     J         election. 

[abitti 
,  and 
regat 
iredh 
:h  hat 

(10)  Geological  partition.ic 

(11)  Artificial  partition. 

•'ll 

53 

a.'-'  "•5.T: 

c.   Regressive  partition. 

t.  Regressive  election. 

(S 

w.  Indiscriminate  partition. 

y.  Indiscriminate  failure. 

c-^^ 

(F)  Racial  demarcation  through  isol 

a  tion. 

(H)   Racial  intensification  through   survival          ' 

4:  s::: 
u3  ^ 

(through  selection  when  discriminate). 

ila- 

d.  Reflexive  isolation. 

j.   Reflexive  selection. 

1 

§1^ 

5.  Conjunctional  isolation. 

15.   Conjunctional  selection. 

l:-g 

(12)  Sexual  isolation. 

(40)  Sexual  selection. 

SO« 

(13)  Social  isolation. 

(41)  Social  selection. 

:;o-2 

6.   Impregnational  isolatioa 

(42)   Filio-parental  selection. 

2  3  =» 

(14)  Dimensional  isolation. 

1 6.   Dominational  selection. 

*  £  b. 

(15)  Structural  isolation. 

w 

(43)  Sustentational  domination. 

Physio-   (^(16)   Potential  isolation, 
logical   -{(17)  Segregate  fecundity. 

(44)   Protectional  domination. 

> 

(45)   Nidificational  domination. 

=  c-^ 

isolation '(18)   Segregate  \-igor. 

0 

(46)   Mating  domination. 

II  "Ho 

(19)  Segregate  adaptation 

0 

^    i. 

(47)   Prepotential  domination. 

< 

gss 

(20)  Segregate        freedom 

a 

17.   Impregnational  selection. 

> 

IP 

from  competition. 

1 

(48)   Dimensional    reflexive    se- 

e 

SI    ex  at 
b    V    w 

(21)  Segregate     escape 

0^ 
p 

lection. 

^    1 

§5?"2 

from  enemies. 

c 

(49)  Structural  reflexive  selection. 

0 
3 
0" 

«^5 

7.  Institutional  isolation. 

a 

1" 

(50)   Potential  selection. 

r  e.  Environal  isolation. 

(51)   Fecundal  selection. 

2. 

■"£3-2 

8.   Endonomic  isolation. 

? 

18.   Institutional  selection. 

n 
n 

ES=2 

(22)   Industrial  isolation. 

0 

u 

(52)  Ecclesiastical  selection. 

0' 

is^l 

(23)  Chronal  isolation. 

^ 

(53)   Militar>-  selection. 

3 

Sss- 

B 

Seasonal  isolation. 

B 

(54)  Sanitary  selection. 

=>i-g 

1 

Cyclical  isolation. 

•§ 

(55)   Penal  selection. 

■•    .5  * 

e 

(24)  Migrational  isolation.  . 

1 

19.   Prudential  selection. 

g«^§ 

« 

■q 

k.  Environal  selection. 

:S>S3 

a  • 

9.   Heteronomic  isolation.       .. 

U 

20.   Endonomic  selection. 

S'l^J 

CI 

2 

(25)  Transportational  iso- 

(56)  Habitudinal  selection 

&.§-2 

■3 

8 

lation,  x 

S3^ 

(57)  Aptitudinal   selection 

4j  ^         C/ 

0 

(26)  Geological  isolation.* 

S.3 

■' 

•ailS 

0 

(27)  Pertilizational    isola- 

0 g.  f> 

21.  Heteronomic  selection.      \     VIII.   He- 

.3  c^_ 

tion. 

a«[T 

(58)   Natural  selection.         >■     teronomic 

«2§1 

(28)   .\rtificial  isolation. 
/.  Regressive  isolation. 

' 

(59)   Artificial  selection.      •'      selection. 

«:  a  h 

/.  Regressive  selection. 

-< 

L 

2.  Indiscriminate  elimination. 

X.  Indiscriminate  isolation. 

t"  .22 

a  C 

^    C8 
at    o 

**  <u 

e  c 

o  .S 

t5  ••-' 

d  4> 

•o  > 

O    ctf 

8.1 

OS     C3 
£1    « 


•§ 


TABLES     OP     FORMS.  1 39 

3.    The  Forms  of  Selection  Defined. 

Reflexive  selection,  based  on  relations  within  the  group. 

*ti5.  Conjunctional  selection,  '.'  cooperation  of   individuals  especially  *."  the 

coordination  of  instincts  and  habits  with  quaUties.  j^ 

(40)  Sexual  selection  '.'  coordination  of  sexual  instincts  and  quaUties.  g, 

(41)  Social  selection  '.'  coordination  of  social  instincts  with  quaUties.  a 
*t(42)  Filio- parental  selection  '.'  coordination  between  the  powers  and  char-  § 

acters  of  the  parents,  and  the  size,  number,  form,  and  instincts  of  the 
young. 
i6.  Dominational  selection  *.'  power  to  outdo,  outrun,  and  overcome  others 

of  the  same  group  in  appropriating  needed  resources.  » 

(43)  Susientational  domination  '.'  taking  food.  g* 

(44)  Protectional  domination  '.'  taking  positions  affording  safety. 

(45)  Nidificational  domination  • .'  taking  positions  for  breeding.  3 

(46)  -\/a/i»gd£>m«na<uw  ".•  monopolizing  mates.  ^ 

(47)  Prepotential  domination  " .'  superior  potency  of  poUen. 
♦17.  Impregnational  selection  '.'  structural  and   physiological  coordinations       *< 

that  secure  a  suflBciency  of  impregnated  germs  with  least  waste.  r    S^ 

(48)  Dimensional  selection  ".'  coordination  in  length  of  pistils  and  pollen 
tubes,  and  in  size  of  other  impregnating  organs.  g- 

(49)  Structural  selection  "."  coordination  of  clasping  organs,  etc 

(50)  Potential  selection  '."  coordination  of  the  sexual  elements. 

(51)  Fecundal  selection  '.'  coordination  in  thcrelative  number  of  the  male 
and  female  elements  preventing  waste.  §. 

fiS.  Institutional  selection  '.'  suppression  of  reproduction  for  (52)  Eccle- 
siastical, (53)  MiUtary,  (54)  Sanitary,  and  (55)  Penal  reasons;  or  the 
favoring  of  certain  types.  f^ 

fig.  Prudential  selection  '.'  delay  of  marriage  and  prevention  of  reproduction 

for  economic  and  other  personal  reasons. 

Environal  selection  "."  relations  of  the  group  and  the  environment.  S 

20.  Endonomic  selection,  determined  by  activities  in  the  group.  3* 

t(56)  HabHudinal  selection,  determined  by  acquired  habitudes. 


o. 


sr 


p 


o 
*(57)  Aptiiudinal  selection,  determined  by  innate  aptitudes.  ^ 


J21.  Heteronomic  selection,  determined  by  activities  in  the  environment.  1    ++ 

(58)  Natural  selection,  determined  by  the  irrational  environment.  y  ^ 

(59)  Artificial  selection,  determined  by  the  rational  environment.  J    i" 

§/.  Regressive  selection,  as  when  accommodation  preserves  those  of  inferior  racial 
endowments. 


Explanation  of  the  signs  used  in  Sections  2  and  3. 

=  Equal  to.    +  Combined  with. 

'."  By  means  of;  produced  by;  through. 

*    Determined  by  previously  attained  aptitudes. 

t    Determined  by  previously  attained  habitudes. 

*t  Determined  by  aptitudes  and  habitudes. 

J    Determined  by  conditions  in  the  present  environment. 

§    Determined  by  one  or  more  of  these  influences. 


I40  CLASSIFICATION   OF   THE   FORMS   OF  THE   PRINCIPLES. 

4.  Conditions  Determining  the  Forms  0}  Selection. 

The  forms  of  selection  depend  on  the  following  conditions  (the 
letters  and  numbers  are  those  used  in  the  tables  on  pages  138-139) : 

y.  The  relations  in  which  individuals  of  the  same  group  stand  to 
each  other;  that  is,  the  reflexive  conditions.  First,  the  aptitudes  (i.  e., 
instincts  and  other  inherited  powers),  that  shape  these  relations  to 
each  other;  second,  the  habitudes  (i.  e.,  habits  and  other  acquired 
powers),  that  shape  their  relation  to  each  other;  and,  third,  the 
physical  characters  of  the  individuals,  must  be  coordinated. 

k.  The  relations  in  which  the  group  stands  to  the  environment,  that 
is,  the  enviroiial  conditions  (arising  from  the  action  and  reaction  be- 
tween the  group  and  its  environment),  must  be  harmonized. 

20.  The  conditions  within  the  group  that  shape  these  relations  to 
the  environment;  that  is,  "the  endonomic  conditions,  being  (56)  the 
habitudes,  and  (57)  the  aptitudes  that  enable  the  isolated  group  to 
determine  how  it  will  use  the  environment,  must  be  kept  in  the  fullest 
possible  accord  with  these  uses  and  with  each  other. 

21.  Heteronomic  conditions,  (58)  natural  and  (59)  artificial;  that  is, 
conditions  in  the  environment  that  constitute  a  limit  to  the  possible 
methods  of  escape  from  destruction.  Small  colonies  of  Hawaiian 
snails,  of  the  same  species,  isolated  in  neighboring  valleys,  but  occu- 
pying the  same  species  of  trees  and  feeding  in  the  same  way,  and  all 
exposed  to  the  same  enemies,  it  seems  to  me  are  probably  subject  to 
the  same  forms  of  heteronomic  environal  selection.  Any  snail, 
capable  of  living  on  several  species  of  trees  growing  in  thick,  shady 
groves,  when  brought  to  a  valley  where  only  one  species  of  such  trees 
is  found,  is  subjected  to  heterono7nic  conditions,  for  but  one  method 
of  survival  is  open  to  it.  But  even  under  these  conditions  we  find 
divergence  taking  place  in  isolated  groups.  Shall  we  attribute  such 
divergence  to  diversity  of  selection  or  to  the  diversity  presented  in 
the  average  character  of  the  groups  when  first  isolated?  I  believe 
this  latter  explanation  is  the  more  reasonable.  If  each  colony  was 
originated  by  a  single  snail,  avc  know  it  is  impossible  that  these  original 
progenitors  of  the  different  colonies  should  in  every  respect  have 
possessed  the  same  characters.  It  is  also  impossible  that  the  varia- 
tions occurring  in  an  isolated  colony  springing  from  a  single  pair 
should  be  exactly  the  same  variations,  presented  in  exactly  the  same 
proportions,  as  in  the  mother  colony  from  which  they  were  separated. 

The  influences  determining  the  forms  of  isolation,  partition,  and 
election  are  also  presented  under  the  aspects  of  reflexive  influences 
and  environal  influences,  and  in  constructing  terras  for  the  different 


AUTONOMIC   AND   HETERONOMIC    INFLUENCES.  I4I 

forms  of  these  three  principles  we  are  able  to  avail  ourselves  of  the 
adjectives  that  have  been  used  in  designating  the  different  forms  of 
selection.  This  is  a  great  aid  in  presenting  the  relations  between  the 
four  principles  in  their  different  forms. 

In  many  of  the  places  where  the  sign  •."  (meaning  caused  by)  is  used 
after  the  forms  of  reflexive  selection,  it  might  with  equal  correctness 
be  changed  to  .'.  (meaning  causing).  For  example,  social  selection 
may  be  described  on  the  one  hand  as  depending  on  the  coordination 
of  social  instincts  and  qualities,  and  on  the  other  hand  as  building 
up  and  maintaining  the  social  instincts  and  the  characters  on  which  they 
depend.  Taking  a  special  case:  Without  any  possible  method  of 
recognizing  each  other  there  could  be  no  social  selection ;  but,  on  the 
other  hand,  when  a  new  race  is  formed,  it  is  social  selection  that  seizes 
on  some  new  and  fluctuating  character,  emphasizing,  intensifying, 
and  rendering  it  permanent;  and  so,  in  an  important  sense,  it  may  be 
said  that  social  selection  produces  the  recognition  marks  and  calls 
and  coordinates  them  with  the  special  instincts  of  the  race  that  recog- 
nize these  marks  and  respond  to  these  calls. 

II.   Autonomic  and  Heteronomic_  Influences. 
1 .   A  utonotnic  Influences  Include  Endonomic  and  Reflexive  Influences. 

The  nomenclature  given  in  this  volume  calls  attention  to  the  fact 
that  endonomic  selection  is  determined  by  habitudes  and  aptitudes  for 
dealing  with  the  environment,  and  is  subject  to  diversity  without  any 
corresponding  diversity  in  the  environment;  and  that  the  forms  of 
reflexive  selection  are  determined  by  the  necessity  for  sexual,  social, 
and  other  coordinations  between  the  members  of  the  same  intergen- 
erating  group,  also  undergoing  change  without  reference  to  change 
in  the  environment.  The  forms  of  endonomic  and  reflexive  selection 
are,  therefore,  brought  together  under  the  term  autonomic  selection, 
which  sets  them  in  strong  contrast  with  heteronomic  selection,  which 
is  always  determined  by  conditions  in  the  environment  surrounding 
the  intergenerating  group.  •  But  the  effects  of  changes  of  activities 
within  the  intergenerating  group,  and  not  depending  on  changes  in 
the  environment,  are  not  all  covered  by  autonomic  selection.  We 
must  also  consider  the  autonomic  forms  of  isolation,  election,  and 
partition,  for  they  are  all  of  importance  in  segregating  and  molding 
the  types  of  allogamic  organisms. 

Autonomic  isolation  includes  both  endonomic  isolation,  produced 
by  industrial,  chronal,  and  migrational  isolation,  and  reflexive  isola- 
tion, produced  by  sexual  and  social  instincts,  by  impregnational 
incompatibilities,  and  by  institutional  requirements.  It  is  in  contrast 
with  heteronomic  isolation,  which  is  determined  by  conditions  outside 


142  CLASSIFICATION   OP   THE    FORMS   OF  THE   PRINCIPLES. 

of  the  organic  group,  as,  for  example,  geological  subsidence,  or  causes 
resulting  in  transportation  to  an  isolated  position. 

Autonomic  selection  cooperating  with  autonomic  isolation  produces 
autonomic  generation;  and  heteronomic  selection  cooperating  with 
heteronomic  isolation  produces  heteronomic  generation. 

Autonomic  election  includes  endonomic  election,  produced  by  the 
success  of  different  acquired  methods  of  dealing  with  the  environment, 
and  reflexive  election,  produced  by  the  social  promotion  or  suppression 
of  individuals  according  to  the  success  of  their  habits  in  relation  to 
others  of  the  same  group.  It  is  in  contrast  with  heteronomic  election, 
which  is  determined  by  conditions  outside  of  the  organic  group. 

Autonomic  partition  includes  endonomic  partition  and  reflexive 
partition,  and  secures  the  grouping  of  individuals  as  regards  their 
habitudes,  through  the  influence  of  activities  that  lie  within  each  asso- 
ciating group.  It  is  in  contrast  with  heteronomic  partition,  which  is 
the  grouping  of  individuals  as  regards  their  habitudes,  through  the 
influence  of  activities  in  the  environment. 

Autonomic  partition  combining  with  autonomic  election  produces 
autonomic  association;  and  heteronomic  partition  combining  with 
heteronomic  election  produces  heteronomic  association. 

Hahitudinal  intensification  may  arise  from  activities  entirely  within 
the  group  of  organisms,  of  which  social  promotion  and  social  suppres- 
sion* of  habitudes  are  familiar  examples,  and  the  combined  effects  of 
these  activities  on  the  habitudes  of  the  group  is  appropriately  called 
autonomic  election ;  but  we  need  a  term  to  designate  the  combined 
influence  of  autonomic  election  and  autonomic  selection,  producing 
the  intensification  of  inherited  aptitudes,  in  addition  to  the  intensifica- 
tion of  acquired  habitudes.  Such  a  term  is  autonomic  intensification. 
It  signifies  the  molding  of  types  by  activities  within  the  intergene- 
rating  and  associating  group.  In  contrast  with  autonomic  intensifi- 
cation, we  have  intensification  produced  by  the  combined  action  of 
heteronomic  election  and  heteronomic  selection,  which  may  appro- 
priately be  called  heteronomic  intensification. 

The  cooperation  of  autonomic  partition  and  autonomic  isolation 
I  call  autonomic  demarcation;  and  the  cooperation  of  heteronomic 
partition  and  heteronomic  isolation  I  call  heteronomic  demarcation. 

The  cooperation  of  autonomic  intensification  with  autonomic 
demarcation  produces  autonomic  segregation;  and  the  cooperation  of 
heteronomic  intensification  with  heteronomic  demarcation  produces 
heteronomic  segregation. 


♦Baldwin  defines  social  suppression  as  "Suppression  of  the  socially  unfittest  by 
law,  custom,  etc."     (See  "Social  and  Ethical  Interpretations,"  Appendix  B.) 


PARTITION   CONTROLLING   ISOLATION.  1 43 

2.  Autonomic  Partition  Prodiices  Autonomic  Isolation. 

In  the  evolution  of  the  European  races  of  man  the  tendencies  which 
break  down  ancient  segregation,  whether  resting  on  habitudes  or 
aptitudes,  are  so  strong  that  it  is  difficult  for  us  to  apprehend  the 
conditions  of  society  in  which  segregative  tendencies  are  in  full  force. 
The  caste  system  of  India  not  only  maintains  with  absolute  strictness 
the  old  barriers  based  on  traditions  received  from  remote  genera- 
tions, but  tends  to  create  new  divisions,  resting  at  first  on  industrial 
habits,  but  in  time  reinforced  by  separate  social  customs,  separate 
ideals,  and  separate  methods  of  training,  and  are  finally  intrenched 
behind  restrictions  forbidding  marriage  with  those  who  were  once 
considered  as  belonging  to  the  same  caste.  Professor  Reinsch  states* 
that  there  are  no  less  than  3,000  castes  in  India;  and  missionaries 
who  have  studied  the  institutions  of  the  country  most  carefully  assure 
us  that  if  a  caste  is  defined  as  an  intermarrying  group  that  is  completely 
excluded  from  marriage  with  all  other  groups,  then  the  castes  of 
India  number  many  thousands.  Of  the  Brahmins,  who  are  considered 
the  highest  caste  of  India,  there  are  over  1,800  such  sub-castes. 

Rev.  J.  P.  Jones,  D.  D.,  of  Pasumalai,  South  India,  informs  me  that 
during  his  residence  in  Southern  India"  a  branch  of  a  certain  barber 
caste  has  taken  up  the  trade  of  weaving ;  and  feeling  that  their  occu- 
pation, which  is  being  transmitted  from  father  to  son,  sets  them  above 
the  barber  caste,  they  are  now  beginning  to  require  that  the  son  of  a 
barber  desiring  to  marry  the  daughter  of  a  weaver  must  give  up  bar- 
bering  and  become  a  weaver. 

The  one  remaining  step  required  for  the  full  establishing  of  the  new 
caste  will  probably  come  within  a  few  years,  and  will  be  the  objecting 
to  additions  to  the  guild  from  those  who  have  not  been  bom  within 
its  ranks.  Though  railroads  and  other  influences  from  Europe  tend 
toward  freer  intercourse,  these  new  castes  are  struggUng  into  exist- 
ence ;  and  the  tendency  is  to  fortify  the  spirit  of  segregation  by  refus- 
ing to  eat  or  have  close  fellowship  with  any  outside  of  the  caste  that 
has  thus  recently  come  into  being. 

The  caste  system  as  developed  in  India  is  as  unlike  the  democratic 
conservatism  of  China  as  it  is  opposed  to  the  progressive  individual- 
ism of  European  races.  It  may  be  doubted  whether  the  caste  system 
of  India  can  ever  develop  into  a  truly  progessive  system.  But  the 
essentially  democratic  life  of  China  stands  in  a  very  different  relation 
to  the  progressive  element  of  European  civilization.  In  innate  racial 
qualities  no  people  can  surpass  the  Chinese ;  and  their  vitality  and 
power  of  adaptation  is  such  that  they  seem  to  be  equally  fitted  for  suc- 


♦  See  "  The  Forum"  for  June,  1901. 


144  CLASSIFICATION   OF  THE   FORMS   OF   THE   PRINCIPLES. 

cess  in  all  climates  and  in  all  countries.  Moreover,  under  the  stimulus 
of  intercourse  with  European  civilization,  there  are  evident  signs  that 
new  and  progressive  elements  will  be  added  to  the  old  ideals  till  a  truly 
progressive  spirit  is  attained.  The  remarkable  power  of  accommoda- 
tion to  different  climates  and  health  conditions  possessed  by  the  race, 
especially  by  the  branch  occupying  the  southern  provinces  of  China, 
is  such  that  few  races  are  able  to  endure  free  competition  with  them 
even  when  the  country  and  climate  are  so  chosen  as  to  give  the  best  pos- 
sible chance  to  their  rivals.  Members  of  the  Teutonic  race,  when  sub- 
•  jected  to  the  climate  of  India,  suffer  from  the  effects  of  the  heat ;  and 
their  small  power  of  individual  adaptive  modification  in  that  direction 
gives  them  but  little  prospect  of  becoming  completely  adapted  through 
the  effects  of  natural  selection;  for,  if  their  children  remain  contin- 
uously in  the  country,  they  have  not  sufficient  energy  for  the  battle  of 
life.  On  the  other  hand,  the  Chinese  from  Canton,  with  high  powers 
of  accommodation,  are  fully  successful  as  permanent  settlers,  both  in 
the  cold  of  Manchuria  and  in  the  heat  of  the  Malay  Peninsula,  Borneo, 
and  the  Philippine  Islands,  and  if  completer  racial  adjustment  is 
needed,  they  are  sure  to  attain  to  it  in  the  course  of  generations,  through 
the  accumulation  of  coincident  variations. 

In  the  last  chapter  of  his  Problems  of  Evolution,  Headley  discussed 
from  a  biological  point  of  view  some  of  the  problems  arising  in  the 
intercourse  of  eastern  and  western  races. 

III.  An  Unwarranted  Assumption. 

In  discussing  the  influences  producing  evolution  some  writers  have 
assumed  that  all  diversity  of  survival  in  different  groups  of  individ- 
uals of  the  same  species  is  due  to  diversity  in  the  environments  to 
which  the  groups  are  exposed;  and  as  natural  selection  is  defined 
as  the  influence  of  the  environment  in  determining  what  individuals 
shall  survive,  the  inference  is  reached  that  diversity  of  natural 
selection  is  the  only  influence  producing  diversity  of  survival.  A 
careful  study,  however,  of  causes  producing  diversity  of  survival  in 
isolated  groups  shows  that  this  assumption  is  without  foundation. 
In  the  first  place,  it  ignores  the  fact  that  diversity  in  sexual  selection,, 
and  in  any  one  of  the  other  forms  of  reflexive  selection,  depends  on 
diversity  in  the  influence  of  members  of  the  group  upon  each  other, 
and  that  these  influences  may  pass  through  a  considerable  range  of 
divergence  without  change  in  the  conditions  lying  outside  of  the 
species.  In  the  case  of  man  the  forms  of  reflexive  selection  depend 
chiefly  on  the  form  of  social  organization,  which  may  be  subject  to 
great  change  without  reference  to  change  in  the  environment  of  the 


AN   UNWARRANTED  ASSUMPTION.  1 45 

group.  In  the  second  place,  it  ignores  the  fact  that  diversity  of  envi- 
ronal  selection  may  be  brought  about  either  by  diversity  in  the  activ- 
ities of  the  environment  (that  is  by  heteronomic  selection),  or  by 
diversity  in  the  organism  determining  its  methods  of  dealing  with 
the  environment  (that  is,  by  endonomic  selection). 

Small  differences  may  of  course  be  found  in  the  conditions  presented 
in  any  two  isolated  positions ;  but  when  the  divergence  in  the  groups 
of  organisms  is  not  in  accord  with  nor  in  proportion  to  these,  it  can  not 
be  attributed  to  them.  If,  however,  we  find  that  the  form  of  selec- 
tion is  determined  by  the  methods  of  using  the  environment  adopted 
by  the  group,  and  that  this  is  determined  by  the  innate  aptitudes  of 
the  individuals  that  founded  the  colony,  I  call  the  principle  aptitudinal 
selection.  If  again,  the  method  of  using  the  environment,  and  so  the 
form  of  selection,  is  determined  by  the  training  and  acquired  habits 
of  those  founding  the  group,  I  call  the  principle  habitudinal  selection. 

Still  further,  there  are  strong  reasons  for  believing  that  divergent 
forms  of  survival  may  arise  in  isolated  groups,  not  only  when  the  envi- 
ronment surrounding  each  group  is  the  same,  but  when  the  habitudes 
and  aptitudes  of  the  individuals  establishing  the  groups  are  the  same. 
If  we  select  two  islands  as  completely  alike  in  climate  and  resources 
as  can  be  found,  and  plant  upon  the  same  two  colonies  of  a  few 
families  each,  selected  in  such  a  way  that  the  average  character  of 
the  colonies,  in  both  innate  and  acquired  characteristics,  shall  be  as 
much  alike  as  possible,  and  if  we  then  subject  them  to  complete  iso- 
lation from  each  other  and  from  the  rest  of  the  world,  will  they  not  in 
a  few  generations  become  divergent  in  language,  in  dress,  in  customs, 
in  industries,  and,  if  the  experiment  is  continued  through  scores  of  gen- 
erations, even  in  race  characters?  This  might  be  called  spontaneous 
diversity  of  election  in  partitioned  groups,  producing  divergence 
of  habitudes,  and  finally  divergence  of  habitudinal  selection,  and  so 
divergence  in  race  characters. 

In  Professor  Conn's  Methods  of  Evolution,  1900,  will  be  found  a 
very  lucid  statement  of  the  importance  of  isolation  as  a  primal  factor 
in  all  divergent  evolution ;  but  his  plan  of  exposition  aims  at  giving 
in  broad  outlines  the  main  factors,  rather  than  a  complete  analysis 
of  the  influences  producing  each. 


CHAPTER  IX. 

SUMMARY  AND   CONCLUSION. 
I.  Summary.     . 
1.  Segregation. 

As  segregate  breeding  is  the  fundamental  principle  producing  racial 
segregations,  and  as  isolation  and  selection  cooperate  in  controlling 
the  degrees  and  forms  of  segregate  breeding,  and  therefore  in  control- 
ling variation  and  heredity,  so  also  it  will  be  found  that  segregate 
association  is  the  fundamental  principle  producing  habitudinal  segre- 
gation, and  so  partition  and  election  cooperate  in  controlling  the  forms 
of  segregate  association,  and  therefore  in  controlling  innovation  and 
tradition. 

It  is  also  evident  that  the  initial  racial  segregation  introduced  by 
discriminate  isolation,  or  by  the  indiscriminate  isolation  of  a  few  pairs, 
may  be  greatly  hastened  and  intensified  by  the  exposure  of  the  isolated 
groups  to  diverse  forms  of  selection ;  and  it  is  no  less  certain  that, 
even  when  the  environment  is  virtually  the  same,  diverse  forms  of 
selection  may  be  introduced  by  diverse  methods  of  using  the  environ- 
ment that  are  liable  to  be  adopted  by  the  isolated  groups.  Moreover, 
it  is  equally  evident  that  the  initial  habitudinal  segregation  intro- 
duced by  discriminate  partition,  or  by  the  indiscriminate  partition  of 
a  single  pair,  may  be  greatly  hastened  and  intensified  by  the  exposure 
of  the  separated  groups  to  diverse  forms  of  election  arising  from  the 
various  forms  of  success,  which  are  determined  by  the  activities  that 
become  habitual  in  each  group. 

The  evolution  of  organic  types  is  originated  and  maintained  by 
partition  and  election  producing  habitudinal  segregation,  and  by 
isolation  and  selection  producing  racial  segregation.  Without  these 
principles  producing  their  intensifying  and  ramifying  effects  on  organic 
types,  the  complex  world  of  life  could  never  have  arisen  out  of  the 
simple  forms  of  primitive  life;  and  without  the  continuance  of  the 
segregations  thus  produced  the  diversity  that  has  been  reached  would 
soon  be  dissolved  and  the  whole  world  of  life  would  be  reduced  to 
but  one  species.  But  the  history  of  races  and  species  shows,  on  the 
one  hand,  that  segregate  breeding  when  fully  fortified  by  physiologi- 
cal and  psychological  incompatibilities  is  never  removed ;  and,  on  the 
other  hand,  that  whenever  increasing  stringency  of  segregate  breed- 
ing is  in  any  way  introduced,  there  we  have  either  the  transforma- 

147 


148  SUMMARY   AND  CONCLUSIO^f. 

tion  of  some  existing  species  or  the  setting  apart  of  new  groups  that 
grow  into  new  species  unless  reabsorbed  by  crossing  or  exterminated 
by  competition. 

*  The  whole  process  of  bionomic  evolution,  whether  progressive  or 
retrogressive,  whether  increasingly  ramified  and  divergent,  or  increas- 
ingly convergent  through  amalgamation,  is  a  process  by  which  the 
limitations  of  segregate  breeding  are  either  set  up  and  established  or 
cast  down  and  obliterated.  But,  as  we  have  already  seen,  on  the  side 
of  amalgamation  an  impassable  barrier  is  in  time  reached  in  the 
physiological  and  psychological  incompatibilities  of  long-established 
types,  while  on  the  side  of  advancing  segregation  the  possibilities  are 
constantly  increasing.  The  general  result  is  that  new  isolations 
and  incompatibilities  are  constantly  arising,  forming  new  races  and 
species,  which  in  time  become  so  divergent  that  it  is  impossible  for 
them  to  coalesce  under  any  conditions. 

2.  Unbalanced  Propagation. 

If  we  wish  to  find  a  principle  which,  if  continued  from  generation  to 
generation,  will  steadily  tend  towards  the  transformation  of  type,  it 
is  unbalanced  propagation  continuously  of  the  same  sign.  That  is, 
if  the  result  desired  is  increase  of  the  character  under  consideration, 
the  selection  in  successive  generations  must  be  of  those  individuals 
that  possess  the  character  in  more  than  the  average  degree ;  and  such 
selection  may  be  said  to  be  continuously  of  the  plus  form.  If  the  in- 
dividuals selected  in  each  generation  depart  from  the  type,  but  are  so 
selected  that  those  above  the  average  are  exactly  sufficient  to  balance 
those  from  below  the  average,  the  average  character  of  the  mixing 
mass  will  be  the  same  as  the  average  of  the  original  stock ;  and  again, 
if  the  selection  is  plus  in  one  generation  and  equally  minus  in  the  next 
generation,  the  result  will  be  uncertain,  even  though  long  continued, 
for  the  effects  of  selection  in  one  generation  will  be  balanced  by  the 
effects  of  selection  in  the  next  generation,  and  we  shall  have  one  form 
of  balanced  selection.  With  a  definition  of  balanced  propagation  that 
includes  balancing  of  both  the  kinds  just  mentioned,  we  may  say  with 
confidence  that  unbalanced  propagation,  if  continuous,  will  produce 
transformation,  and  that  balanced  propagation  of  the  type,  if  con- 
tinuous, will  produce  stability  of  type,  and  that  balanced  propagation 
of  forms,  some  of  which  are  considerably  above  the  type  and  others 
of  which  are  considerably  below  the  type,  will  produce  fluctuating 
variation. 

We  may  next  ask,  how  is  unbalanced  propagation  brought  about  ? 
The  answer  is  that,  in  both  natural  and  artificial  breeding,  it  may  be 


UNBALANCED   PROPAGATlOlSf.  14^ 

brought  about  either  by  the  unbalanced  effects  of  the  processes  sepa- 
rating the  individuals  into  coexistent  groups  that  are  prevented  from 
intergenerating,  or  by  the  unbalanced  effects  of  differing  degrees  of 
survival  for  different  forms  of  variation.  The  former  principle  is  called 
"isolation,"  and  the  latter  principle  "selection."  It  is  quite  evident 
that  in  as  far  as  selection  prevents  any  form  from  propagating,  in  so 
far  it  prevents  intergeneration  between  that  form  and  the  forms  that 
produce  the  next  generation ;  but,  at  the  same  time,  I  prefer  to  define 
isolation  as  the  prevention  of  free  crossing  between  coexisting  groups, 
though  the  individuals  of  each  group,  so  far  as  they  survive,  are 
freely  intergenerating.  When  pointing  out  the  correspondences 
between  selection  and  isolation,  I  would  say  that  both  are  principles 
by  which  the  abiding  principle  of  segregate  breeding  is  modified 
and  intensified;  and  that  when  either  of  them  produces  unbalanced 
propagation  effected  by  the  same  sign  in  successive  generations,  the 
result  is  transformation  of  type. 

During  the  process  of  domestication  the  reproductive  powers  of 
many  species  are  so  impaired  that  it  is  with  difficulty  that  a  perma- 
nent domestic  race  can  be  produced.  Many  individuals  that  thrive 
on  the  nourishment  furnished  fail  to  leave  offspring,  so  that  the  race 
is  perpetuated  not  by  the  offspring  of  those  which  are  most  pleasing  to 
those  who  keep  and  select  them,  but  by  the  offspring  of  those  which 
have  offspring.  The  same  principle  may  produce  transformation  in 
species  that  are  not  under  domestication.  For  if,  among  the  many 
varieties,  there  arises  one  that,  while  retaining  equal  adaptation,  is 
more  fruitful  than  other  varieties,  it  will  be  favored  by  fecundal  selec- 
tion. The  descendants  of  the  most  fertile  will  have  the  largest  share 
in  producing  the  next  generation.  This  will  tend  to  produce  increas- 
ing fecundity  in  succeeding  generations.  This  is  a  form  of  discriminate 
survival ;  but  we  must  remember  that  this  fecundal  selection  will  pro- 
duce accumulation  of  other  characters  besides  fecundity  only  when 
fecundity  is  correlated  with  certain  variations  that  do  not  represent 
the  typical  or  average  form ;  that  is,  only  when  it  is  unbalanced  fecun- 
dity. This  seems  to  be  a  necessary  law.  As  a  corollary  from  this  law, 
I  judge  that,  in  a  stable  intergenerating  species  or  variety,  the  aver- 
age form  will  be  found  to  be  most  fertile ;  or,  at  least,  the  forms  that 
depart  from  the  average  will  not  be  continuously  endowed  with  higher 
fertility  than  the  average  form.  In  considering  the  effect  of  selective 
survival  we  have  to  discriminate  between  balanced  and  unbalanced 
selection.  Unbalanced  selection  is  either  the  selection  of  individuals 
above  the  average  producing  an  increase  of  the  character  thus  selected 
or  the  selection  of  individuals  below  the  average  producing  a  decrease 


I50  SUMMARY  AND  CONCLUSION. 

of  the  character  thus  discriminated  against.  Balanced  selection  is 
usually  secured  by  selecting  individuals  of  the  average  form,  and 
tends  to  produce  increasing  stability. 

3.  Cumulative  Effects  through  the  Cooperation  of  Different  Principles. 

Two  or  more  of  the  factors  mentioned  in  this  volume  may  co- 
operate in  rendering  a  type  more  stable,  or  in  rendering  its  previously 
attained  characters  more  intense,  or  in  diminishing  its  present  char- 
acteristics while  others  are  brought  into  prominence.  If  the  organ- 
isms under  consideration  form  but  one  intergenerant,  any  transforma- 
tion thus  produced  will  be  monotypic ;  but  if  through  the  cooperation 
of  isolation  they  form  several  intergenerants,  any  subsequent  trans- 
formation will  result  in  polytypic  evolution. 

Again,  if  each  factor  working  by  itself  would  tend  to  produce  the 
same  result,  the  united  influence  of  several  factors  working  together 
will  be  much  more  decisive  than  that  of  but  one  of  them  working  alone. 

4.  Cumulative  Effects  through  the  Operation  of  the  Same  Principle  in 
Successive  Generations. 

Once  more  it  should  be  noted  that  the  effect  of  unbalanced  selection 
when  continued  through  many  successive  generations  is  vastly 
greater  than  when  lasting  but  for  one  generation.  Indeed,  on  reflec- 
tion it  becomes  apparent  that  the  great  difference  between  selective 
survival  and  non-selective  survival  is  that  the  former  is  continuous 
from  generation  to  generation,  while  the  latter  is  accidental,  and, 
therefore,  not  continuous.  Moreover,  in  non-selective  survival  the 
effects  of  survival  in  any  one  generation  are  liable  to  be  in  a  measure 
neutralized  by  the  effects  of  survival  in  succeeding  generations.  Dis- 
criminate isolation  is  more  effective  than  indiscriminate  isolation 
because  it  is  more  effective  in  bringing  together  in  one  group  a  consid- 
erable number  of  individuals  that  belong  to  the  same  class ;  that  is, 
that  are  either  of  average  character,  or  above  the  average,  or  below  the 
average.  Indiscriminate  isolation  is  less  likely  to  bring  together  a 
special  type  and  to  repeat  the  process  through  many  generations, 
and  is,  therefore,  usually  less  effective  than  discriminate  isolation  in 
producing  transformation. 

The  probability  that  a  cumulative  result  will  be  reached  through 
the  effects  of  indiscriminate  isolation,  dividing  the  whole  species  into 
two  large  and  nearly  equal  groups,  without  the  cooperation  of  selec- 
tion or  without  the  continuous  and  cumulative  effects  of  suetude  (i.  e., 
of  use  or  disuse),  is  very  small;  but  we  must  remember  that  when 
isolation  has  become  effective  in  shutting  out  all  individuals  of  other 
groups,  divergent  selection,  divergent  suetude,  and  different  forms 


SOME   01^  THE   FACTS   EMPHASIZED.  15I 

and  degrees  of  amalgamation  are  liable  to  arise.  This  liability  is 
enhanced  in  case  the  fragment  indiscriminately  separated  is  small; 
for  there  is  then  a  possibility  that,  in  some  one  of  its  habitudes  or 
aptitudes,  it  will  differ  from  the  original  stock  in  such  a  way  as  to 
insure  its  using  the  environment  in  a  somewhat  different  manner.  It 
is  certain  that  isolation  is  a  principle  tending  toward  the  introduction 
of  diversity  not  only  in  the  forms  of  environal  selection  affecting  the 
species,  but  also  in  the  forms  of  reflexive  selection,  of  suetude,  and  of 
amalgamation. 

The  distinction  indicated  by  discriminate  and  indiscriminate  isola- 
tion pertains  only  to  the  generations  when  group-formation  is  being 
shaped  by  additions  brought  in  from  the  parent  stock  or  from  other 
groups,  and  these  are  usually  the  earlier  generations  of  the  new  groups ; 
but  the  influence  of  this  primal  shaping  will  continue  through  subse- 
quent generations. 

The  action  of  discriminate  survival  and  of  suetude  is,  however,  not 
at  all  confined  to  the  earlier  stages  of  group  formation. 

5.  Amalgamation. 

After  a  group  has  been  considerably  differentiated,  combination 
with  other  groups  is  described  as  amalgamation. 

Amalgamation,  or  the  crossing  of  races  that  have  been  segregated 
for  many  generations,  is  a  most  effective  process  for  introducing  varia- 
tion ;  and,  if  the  contrast  is  not  too  great,  for  adding  vigor  to  the  stock. 

6.  Some  of  the  Facts  Em-pliasized  in  this  Volume. 

(i)  That  segregation  is  the  underlying  principle  throughout  the 
whole  process  of  bionomic  evolution. 

(2)  That  the  causes  producing  and  intensifying  segregation  are  quite 
various,  and  can  not  all  be  included  under  the  term  "  selection,"  and 
that  in  seeking  the  causes  of  organic  evolution  we  must  investigate  all 
the  natural  causes  modifying  the  action  of  segregate  breeding. 

(3)  That  some  of  the  most  powerful  influences  in  the  control  of  seg- 
regation are  due  not  to  different  forms  of  activity  in  the  environment, 
but  to  diversity  of  activities  in  the  organism,  and  may,  therefore,  be 
classed  as  forms  of  autonomic  segregation. 

(4)  That  habitudinal  demarcations,  through  partition,  are  the 
initial  forms  of  grouping,  which,  when  intensified  by  election,  produce 
habitudinal  segregations,  and  that  habitudinal  segregations  are  often 
the  controlling  factors  leading  to  racial  segregations. 

(5)  That  in  reflexive  selection  (that  is,  selection  produced  by  the 
relations  of  members  of  a  species  to  each  other),  the  influence  of  the 
environment  in  producing  the  special  result  is  usually  very  obscure. 


152  SUMMARY  AND   CONCLUSION. 

though  there  can  be  no  doubt  that  it  is  sometimes  operative.  Social 
organization  is  often  affected  by  the  conditions  in  the  environment ; 
but  though  the  environment  remains  unchanged,  vast  changes  in 
social  organization  may  take  place.  For  example,  while  remaining  in 
the  same  region,  and  without  special  change  in  the  environment,  a 
tribe  of  men  may  pass  from  the  hunter  stage  of  life,  through  some- 
thing of  pastoral  life,  into  agricultural  and  diversified  industrial  life. 
This  has  probably  been  the  experience  of  the  Chinese  race. 

(6)  That  endonomic  selection,  resting  on  the  power  of  different 
individuals  of  the  same  species  to  deal  with  the  same  environment  in 
different  ways,  is  a  fruitful  cause  of  divergent  evolution  in  isolated 
sections  of  the  same  species.  This  diversity  of  power  is  sometimes 
due  to  diversity  of  aptitudes,  producing  what  I  call  aptitudinal  selec- 
tion ;  and  sometimes  to  diversity  of  training  and  of  habitudes,  pro- 
ducing what  I  call  habitudinal  selection ;  and  at  still  other  times  to 
different  methods  of  using  the  same  aptitudes  and  habitudes,  for 
which  a  suitable  name  has  not  yet  been  suggested. 

(7)  That  organic  (or  coincident)  selection  is  of  great  importance  in 
securing  a  new  adjustment  when  the  organism  is  suddenly  exposed  to 
an  environment  very  different  from  that  to  which  it  was  previously 
adjusted. 

(8)  That  the  indiscriminate  isolation  of  a  small  fragment  of  a  species 
leads  directly  to  the  modification  of  type  in  the  descendants  of  the 
isolated  fragment,  for  the  character  of  a  single  individual  (or  even 
the  average  character  of  several  individuals)  seldom  if  ever  represents 
the  average  character  of  the  original  stock  in  every  respect. 

(9)  That  indiscriminate  isolation  of  a  large  section  of  a  species 
interrupts  the  unifying  influences  of  tradition  and  of  heredity  between 
separated  branches  of  the  original  stock ;  and,  even  though  the  environ^ 
ment  surrounding  each  branch  is  the  same,  the  traditional  method  of 
dealing  with  the  environment  may  in  one  or  in  both  branches  become 
modified,  and  the  separate  branches  be  thus  subjected  to  divergent 
forms  of  endonomic  selection. 

(10)  That  the  indiscriminate  elimination  of  all  but  a  small  fragment 
of  an  intergenerating  group  may  be  an  important  factor  in  introducing 
transformation,  for  one  or  two  individuals  may  not  be  able  to  transmit 
all  the  traditions  of  the  original  group,  or  to  reproduce  in  the  innate 
characters  of  their  offspring  the  unchanged  average  character  of  the 
original  stock. 

(11)  That  advancing  powers  of  accommodation,  cooperating  with 
higher  degrees  of  altruistic  social  organization,  are  in  an  ever-increasing 
measure  setting  aside  both  environal  and  dominational  selection,  and 
so  lowering  the  racial  standards  of  civilized  man. 


A   METHOD   Olf   STUDY.  153 

(12)  That  a  perverted  form  of  prudential  selection  is  threatening 
the  very  existence  of  some  nations  that  are  counted  highly  civilized. 

(13)  That  the  only  remedy  for  these  destructive  tendencies  lies  in 
enHghtened  and  renovated  institutional  and  prudential  selection,  and 
the  wide  adoption  of  higher  ideals. 

( 14)  That  the  most  marked  characteristic  of  modern  human  history 
is  found  in  the  breaking  down  of  many  of  the  minor  segregations,  both 
social  and  racial,  of  previous  eras,  and  the  ever-increasing  intercourse 
between  nations  and  races. 

(15)  That,  notwithstanding  the  general  trend  of  the  new  era,  among 
the  millions  of  India  many  new  castes  have  been  established  during 
the  past  century. 

II.  Conclusion. 
1 .  What  has  been  Gained  by  Recognizing  Hahiticdinal  Segregation  ? 

Having  completed  our  study  of  the  four  principles  of  segregation,  let 
us  turn  to  the  classification  given  in  Appendices  I  and  II,  and  consider 
what  has  been  gained  by  the  distinct  recognition  of  habitudinal  segregation. 
In  Appendix  I  the  combined  action  of  partition  and  election,  produc- 
ing segregate  association  of  individuals  according  to  their  acquired 
characters,  and  of  isolation  and  selection,  producing  segregate  inter- 
generation  of  individuals  according  to  their  innate  characters,  is  pre- 
sented under  the  single  term  "  segregation."  The  action  and  reaction 
between  the  two  spheres  of  segregation  is  not  clearly  presented,  and, 
under  the  nomenclature  there  given,  it  would  be  difficult  to  consider 
all  the  aspects  in  which  this  interaction  is  manifested.  In  Appendix 
II,  assimilational,  stimulational,  suetudinal,  and  emotional  intension 
are  used  to  designate  intensification,  produced  by  the  different  forms 
of  accommodation  and  of  acquired  characters ;  while  other  terms  are 
used  to  designate  the  intensification  produced  by  the  different  forms 
of  unbalanced  propagation,  securing  the  survival  of  certain  types  of 
variation  in  innate  characters.  The  interaction,  however,  between 
habitudes  and  aptitudes  is  not  as  clearly  presented  in  these  earlier 
papers  as  in  the  chapters  of  this  volume. 

2.  A  Method  of  Study  tltat  should  be  fully  Applied. 

1  believe  the  facts  of  distribution  to  which  I  call  attention  are  of 
great  importance,  and  that  the  methods  of  collecting  and  of  exhibiting 
by  which  these  facts  have  been  brought  to  light  is  worthy  of  being 
applied  in  other  fields.  This  method  may  be  regarded  as  a  develop- 
ment of  the  study  of  "centers  of  creation,"  initiated  by  Louis  Agassiz 
and  transformed  by  Darwin,  Wallace,  and  others  into  the  study  of 
geographical  distribution  as  affected  by  migration  and  divergent  evo- 


154  SUMMARY   AND   CONCLUSION. 

lution.  In  order  to  perfect  the  method  it  is  important  that  the  crea- 
tures under  study  should  be  labeled  at  the  time  of  collection  with  the 
conditions  (of  feeding,  etc.)  under  which  each  specimen  was  found, 
and  should  be  exhibited  on  maps  setting  forth  as  fully  as  possible  the 
conditions  presented  by  the  environment  at  each  point.  An  impor- 
tant step  in  this  direction  has  been  made  by  the  late  Professor  Hyatt, 
of  the  Museum  of  the  Boston  vSociety  of  Natural  History,  in  construct- 
ing a  model  of  the  island  of  Oahu,  on  which  the  geographical  relations 
of  the  species  and  varieties  of  snails  from  that  district  may  be  exhib- 
ited. It  would,  however,  be  a  great  gain  if  a  model  (or  at  least  a  map) 
of  the  island  of  sufficient  size  were  so  arranged  as  to  allow  the  shells 
themselves  to  be  placed  upon  it  in  their  true  positions,  instead  of 
being  represented  by  letters  and  numbers.  The  advantage  of  both 
methods  might  be  attained  by  having,  in  addition  to  the  model  of 
the  island  arranged  according  to  Professor  Plyatt's  method,  a  very 
large  map  on  which  the  shells  might  be  placed. 

The  method  might  be  further  improved  by  the  use  of  colors  and 
other  devices  for  indicating  the  species  of  plant  on  which  each  speci- 
men was  found.  The  influence  of  temperature,  humidity,  and  other 
external  conditions,  and  especially  of  the  conditions  interfering  with 
free  crossing,  may  also  be  studied  by  exhibiting  the  average  character 
attained  under  different  stages  of  the  influence  and  the  degree  of  seg- 
regation resulting  from  the  full  action  of  the  combined,  influences. 

The  degrees  of  segregation  that  have  taken  place  in  the  inhabitants 
of  a  series  of  districts  presenting  dififerent  degrees  of  geographical 
isolation  may  also  be  studied  by  the  determination  of  place-modes  by 
statistical  methods.  Information  on  the  mathematical  methods  that 
have  been  applied  to  this  and  other  allied  problems  in  biology  will  be 
found  in  the  works  of  Francis  Galton,  Karl  Pearson,  C.  B.  Davenport, 
and  others,  and  in  "Biometrika,"  a  journal  for  the  statistical  study 
of  biological  problems. 

3.   The  Study  of  Conditions  Favoring  Segregation. 

A  rich  field  for  the  study  of  organisms  under  conditions  favoring 
segregation  will  be  found  in  the  fauna  and  flora  of  island  groups.  The 
most  interesting  conditions  will  appear  where  the  majority  of  the 
species  are  able  to  distribute  themselves  with  some  degree  of  freedom 
from  island  to  island,  while  some  one  organic  form  is  unable  to  pass 
the  water  barriers,  except  on  very  rare  occasions.  In  such  a  region 
we  shall,  I  believe,  always  find  a  series  of  nearly  related  varieties  or  species 
distributed  in  the  midst  of  a  comparatively  uniform  environment.  vSimi- 
lar  results  will  undoubtedly  be  found  wherever  a  group  of  organisms 


AN  EXAMPLE  IN  ACCORD   WITH   THE  THEORY.  1 55 

that  is  variable  but  of  very  limited  powers  of  migration  has  been  for  many 
generations  surrounded  by  a  mass  of  species  possessing  ordinary  powers 
of  variability  and  ordinary  facilities  for  distributing  themselves. 

If  this  prediction  is  found  to  be  in  accordance  with  facts,  it  will 
show  that  the  explanation  of  divergent  evolution  to  which  we  have 
been  led  by  the  investigations  presented  in  the  foregoing  chapters  is 
essentially  correct. 

4.  Prediction  Confirmed  by  Partula  of  Tahiti. 

Since  writing  the  preceding  statement,  I  have  read  with  the  greatest 
interest  Dr.  A.  G.  Mayer's  memoir  on  "Some  Species  of  Partula  from 
Tahiti;  A  Study  in  Variation."  The  conditions  of  variation  and 
migration  which  he  brings  to  light  in  the  case  of  some  of  the  snails  of 
Tahiti  are  a  fine  example  of  the  conditions  which  I  have  found  in  the 
Hawaiian  snails  to  be  most  favorable  for  the  segregation  of  many 
closely  related  forms  within  a  comparatively  limited  district,  each 
section  of  which  presents  essentially  the  same  environment.  These 
conditions  are,  in  the  case  of  the  closely  related  but  divergent  forms,  a 
full  degree  of  variability,  but  a  very  limited  power  of  migration,  and 
in  the  surrounding  species  the  ordinary  endowments  in  regard  to 
variation  and  migration.  Partula  hyalina  is  found  in  all  the  valleys 
of  the  island  of  Tahiti ;  also  on  the  Austral  islands  and  on  one  of  the 
Cook  group.  It  may,  therefore,  have  opportunities  for  migration  that 
are  not  possessed  by  the  other  species  of  Partula  found  on  Tahiti ;  and 
certainly  it  does  not  present  the  tendency  to  variation  in  form  and 
color  which  we  find  in  some  of  these  species. 

Of  these  other  types  I  will  refer  only  to  three  species  which  are 
found  in  four  valleys,  in  which  the  character  of  the  vegetation  is  essen- 
tially the  same.  On  the  north  side  of  the  island  are  three  approxi- 
mately parallel  valleys,  Pirse,  Fautaua,  and  Tipaerui.  The  first  and 
last  of  these  are  about  3  miles  apart,  Pirge  lying  on  the  east  and 
Tipaerui  on  the  west,  while  Fautaua  and  several  narrow  gorges  lie 
between  them.  These  three  valleys  are,  however,  "broad  and  well- 
watered,  and  contain  a  luxuriant  growth  of  wild  plantains  and  Cala- 
dium,  upon  which  the  snails  are  found  in  large  numbers."  Besides 
Partula  hyalina,  mentioned  above  as  found  in  all  the  valleys  of  the 
island,  there  are  two  species  of  Partula  found  in  these  valleys.  Par- 
tula filosa  is  found  only  in  Pirae,  and  though  constantly  dextral  pre- 
sents divers  shades  of  color.  Partula  otaheitana  is  found  in  all  three 
of  the  valleys,  but  presents  hereditary  tendencies  differing  in  each  of 
the  valleys ;  for  example,  in  Pirae  it  is  constantly  sinistral,  in  Tipaerui  it 
is  constantly  dextral,  and  in  Fautaua  dextral  and  sinistral  forms  are 
found  in  nearly  equal  numbers. 


156  SUMMARY  AND  CONCLUSION. 

On  the  south  side  of  the  island,  about  27  miles  from  the  three 
valleys  just  mentioned,  is  the  valley  of  Vaihiria,  where  Partula  sinis- 
trorsa  is  found.  This  species,  though  closely  related  to  the  two  species 
last  mentioned,  has  adopted  a  different  habit  of  feeding.  "The 
Caladium  and  the  wild  plantain  grow  here  in  abundance,  but  most  of 
the  snails  were  found  upon  the  wild  turmeric,  almost  none  being  dis- 
covered upon  the  Caladium,  and  but  few  upon  the  leaves  of  the  wild 
plantain."  It  is  very  variable  in  color,  but  easily  distinguished  from 
those  of  similar  color  in  the  valleys  first  mentioned  by  its  lack  of  a 
tooth  on  the  body  whorl,  by  its  relatively  thin  and  fragile  lip,  by  its 
more  constricted  suture,  and  by  the  lack  of  variation  in  the  color  of 
the  young.  Of  its  individuals  90  per  cent  are  sinistral  and  10  per  cent 
dextral. 

From  these  facts  Doctor  Mayer  draws  the  following  conclusions: 

Partula  hyalina  is  very  stable  in  all  of  the  valleys,  and  gives  rise  to  no  varieties. 
All  the  other  species,  however,  are  remarkably  variable,  and  give  rise  to  numerous 
color-sports.  These  color-sports  tend  to  breed  true  to  themselves,  and,  therefore, 
to  originate  new  color-forms  and  finally  new  species.  This  tendency  is,  however, 
held  in  check  by  frequent  inter-crossing  with  the  parent  stock,  and  becomes 
effective  only  when  the  new  color  variety  is  isolated,  or  when  it  displays  a  remark- 
ably strong  tendency  to  breed  true.  *  *  *  It  is  probable  that  geographical 
isolation  plays  a  most  important  part  in  the  formation  of  new  species.  If  two 
valleys  be  adjacent,  their  snails  are  closely  related  each  to  each,  whereas  the  wider 
the  separation  between  any  two  valleys  the  more  distant  the  relationship  between 
their  snails.  The  ridges  between  the  valleys,  being  either  barren  or  covered  with 
vegetation  unsuitable  to  the  snails,  afford  barriers  over  which  the  animals  must 
find  it  more  or  less  difficult  to  pass.  Thus  the  Partulae  in  the  Tahitian  valleys  arc 
isolated  very  much  as  are  the  Achatinellidae  of  Oahu  in  the  Hawaiian  Islands. 
*  *  *  As  far  as  the  very  limited  observation  of  the  writer  goes,  there  appears 
to  be  no  difference  in  the  character  of  the  snails  in  different  parts  of  the  same  valley. 
The  difference  between  any  two  adjacent  valleys  is,  however,  very  marked. 

The  full  statement  of  these  facts  and  conclusions  will  be  found  in 
Memoirs  of  the  Museum  of  Comparative  Zoology  at  Harvard  College, 
Vol.  XXVI,  No.  2,  published  in  1902. 

5.   Tlie  Power  of  the  Organism  to  Control  its  Relations  to  the  Environment 
Increases  with  the  Stage  of  Evolution  Attained. 

We  have  shown  by  direct  observation  that  it  frequently  happens 
that  the  same  species  of  snails,  when  distributed  in  isolated  groups  in 
districts  furnishing  the  same  environment,  establishes  divergent 
methods  of  dealing  with  the  environment,  and  so  determines  the  form 
of  selection  to  which  it  is  subjected  in  the  different  districts.  More- 
over, this  power  of  the  organism  to  control  its  relations  to  the  environment 
is  found  to  belong  in  a  higher  degree  to  vertebrate  animals,  and  espe- 
cially to  birds  and  mammals,  while  immeasurably  the  highest  power 


TUNTATlVli   VARIATION    WITH   HliKICDlTY.  157 

of  thus  shaping  his  relations  belongs  to  man.  Civilized  man  not  only 
changes  his  relations  to  the  environment,  but  by  agriculture  and  other 
arts  transforms  the  environment  to  suit  his  own  needs.  In  all  its 
action  inorganic  matter  is  completely  indifferent  to  the  character  of 
the  results,  either  within  the  mass  that  is  acting  or  in  things  external 
to  it;  but  organic  life  is,  throughout  all  its  grades,  striving  to  attain 
an  increasing  power  of  race  preservation  under  given  conditions, 
and,  in  its  highest  manifestation  in  man,  it  breaks  largely  away  from 
the  ancient  thraldom,  and  assumes  an  ever-increasing  control  of  the 
environment. 

6.   The  Chief  Method  of  Advance  is  Tentative  Variation  with  Transmission 
to  Offspring  of  tlie  Endowments  of  the  Survivors. 

Throughout  this  whole  struggle  for  ascendency  the  principal  method 
of  advance  is  the  sending  forth  of  various  tentative  experiments  in  the 
form  of  variously  endowed  individuals  presenting  many  methods  of 
dealing  with  the  environment,  each  individual  that  survives  having 
some  influence  on  the  endowments  of  the  next  generation.  This 
law  of  the  survival  of  the  fittest  applies  to  all  from  the  lowest  to  the 
highest;  but  the  qualities  that  constitute  fitness  differ  progressively. 
In  one  stage,  strength  and  such  weapons  as  teeth  and  claws  are  of  the 
greatest  importance ;  in  another  stage,  the  degree  of  intelligence  and 
the  power  to  produce  artificial  weapons  is  the  test;  and,  in  a  still 
higher  stage,  the  power  of  social  organization  and  the  ethical  ideals 
that  form  the  foundation  for  such  organization  become  the  supreme 
necessity  for  survival.  But  throughout  it  is  the  same  law  of  survival, 
the  survival  of  the  fittest,  the  future  continuance  of  those  fitted  to 
continue.  Though  plants  are  without  conscious  purpose,  we  neces- 
sarily regard  their  production  of  flowers  and  seed  as  anticipatory 
action ;  for  the  whole  significance  of  the  process  is  found  in  its  helping 
to  secure  continued  propagation. 

To  an  observer  at  the  equator,  the  sun  rises  and  sets  each  twenty- 
four  hours,  moving  in  a  circle  nearly  perpendicular  to  the  horizon, 
while  to  an  observer  at  the  North  Pole  the  sun  would  rise  and  set  but 
once  in  a  year,  and  in  each  twenty-four  hours  would  move  through  a 
complete  circle  nearly  parallel  to  the  horizon,  traveling,  as  conven- 
tional language  would  say,  from  left  to  right ;  and  to  an  observer  at 
the  South  Pole,  the  same  sun  would  rise  and  set  but  once  in  a  year^ 
and  would  circle  in  the  reverse  direction,  that  is,  from  right  to  left. 
Now,  in  such  a  case  as  this,  we  do  not  say  that  the  cosmic  process  is 
changed.  So  also,  in  the  case  of  ethical  man,  I  would  not  say,  as  Hux- 
ley does,  that  his  life  is  in  opposition  to  the  cosmic  process,  but  rather 
that  he  has  attained  to  one  of  the  higher  stages  of  that  process,  in 
which  the  meek  are  the  ones  who  inherit  the  earth. 


158  SUMMARY   AND   CONCLUSION. 

7.   Accommodation,  Cooperation,  and  Anticipation. 

There  are  three  spheres  in  which  it  is  evident  that  progressive 
adaptation  for  beneficent  action  may  take  place,  commencing  with  the 
smallest  beginnings  in  the  lowest  organisms  and  progressing  through 
each  higher  stage  of  evolution  till  the  widest  reaches  are  attained. 

These  three  spheres  are  acconimodational  action  (whether  tentative 
or  directly  discriminative) ,  CO  /»era/ii;e  action,  and  anticipatory  action. 
Power  for  action  in  these  spheres  is  characteristic  of  the  realm  of 
life,  and  is  manifested  in  higher  and  higher  efficiency  till  accommo- 
dation tries  to  prove  all  things,  holding  fast  that  which  is  good ;  and 
cooperation,  associated  with  division  of  labor  and  community  of 
interest,  reaches  out  to  include  in  its  beneficence  the  living  universe ; 
and  anticipation,  pressing  forward  in  its  unbounded  aspirations  and 
ideals,  becomes  the  ever-advancing  influence  of  foresight  and  predic- 
tion in  the  activities  of  the  highest  beings. 

8.  Increasing  Recognition  of  Autonomic  Factors. 

It  will  be  observed  that  throughout  the  whole  process  of  evolution 
there  are  two  classes  of  factors,  of  which  one  class  may  be  called  hete- 
ronomic,  in  that  they  are  subject  to  change  through  change  in  activi- 
ties lying  outside  of  the  group  of  organisms  concerned,  while  the  other 
class  may  be  called  autonomic,  in  that  they  are  controlled  by  changes 
within  the  group  of  organisms.  In  the  theory  of  evolution  presented 
by  Darwin,  the  importance  of  the  heteronomic  factors  was  empha- 
sized, though  he  pointed  out  one  form  of  autonomic  transformation, 
which  he  designated  by  the  term  "sexual  selection."  To  some  ex- 
pounders of  evolution  natural  selection  has  seemed  so  completely 
sufficient  that  they  have  been  ready  to  deny  the  influence  of  sexual 
selection  (or  of  any  other  autonomic  factor)  in  producing  divergence. 
On  the  whole,  however,  there  has  been  during  the  past  ten  or  fifteen 
years  an  increasing  recognition  of  the  fact  that  not  only  sexual  selec- 
tion but  other  autonomic  factors  are  more  or  less  effective  in  control- 
ling the  forms  of  selection,  and,  therefore,  in  controlling  the  transfor- 
mations of  organisms.  Do  we  not  thus  reach  one  explanation  of  the 
continuous  advance — the  determinate  evolution — of  certain  large 
classes  of  animals  ? 

The  recognition  of  autonomic  factors  in  the  process  of  evolution  is 
giving  new  insight  into  the  self-developing  endowments  of  the  organic 
world. 


APPENDIX  I. 

RKKLEXIVE   SEGREGATION.* 

[A  small  portion  of  "  Divergent  Evolution  through  Cumulative  Segregation."]! 

Reflexive  segregation  is  segregation  arising  from  the  relations  in 
which  the  members  of  one  species  stand  to  each  other. 

It  includes  three  classes,  which  I  call  "conjunctional,"  "impregna- 
tional,"  and  "institutional  segregation." 

It  is  important  to  observe  that  intergeneration  requires  compati- 
bility between  members  of  the  group  in  all  the  circle  of  relations  in 
which  the  organism  stands ;  but,  in  order  to  insure  isolation  between 
any  two  or  more  sections  of  a  species,  it  is  sufficient  that  incompati- 
bility should  exist  at  but  one  point.  If  either  sexual  or  social 
instincts  do  not  accord,  if  structural  or  dimensional  characters  are  not 
correlated,  if  the  sexual  elements  are  not  mutually  potential,  or  if 
fixed  institutions  hold  groups  apart,  intergeneration  is  obstructed  or 
prevented  and  isolation  is  the  result,  either  as  segregation  or  as  sepa- 
ration that  is  gradually  transformed  into  segregation. 

(o)  Conjunctional  Segregation. 

Conjunctional  segregation  is  segregation  arising  from  the  instincts 
by  which  organisms  seek  each  other  and  hold  together  in  more  or  less 
compact  communities,  or  from  the  powers  of  growth  and  segmentation 
in  connection  with  self-fertilization,  through  which  similar  results  are 
gained. 

I  distinguish  four  forms — social,  sexual,  germinal,  and  floral  segre- 
gation. 


*  Under  "  Demarcational  Segregation"  I  class  the  influences  by  which  organ- 
isms are  distributed  in  separate  groups.  It  includes  both  environal  segregation 
and  reflexive  segregation,  and  is  equivalent  to  isolation  as  now  generally  used.  In 
the  section  of  this  paper  on  Environal  Segregation  (not  here  reproduced),  I 
considered  the  forms  of  isolation  arising  from  the  relations  of  the  species  to  the 
environment.  A  classified  table  of  the  forms  of  segregation  will  be  found  near 
the  end  of  this  paper. 

t  Read  December  15,  1887.  From  the  Linnean  Society's  Journal,  Zoology, 
Vol  XX. 

159 


l6o  APPRNDIX    I — DIVERGENT  EVOLUTION. 

10.  Social  Segregation  Produced  by  Discrimhiative  Action  oj  Social  Instincts* 

The  law  of  social  instinct  is  preference  for  that  which  is  familiar  in 
one's  companions;  and  as  in  most  cases  the  greatest  familiarity  is 
gained  with  those  that  are  near  of  kin,  it  tends  to  produce  breeding 
within  the  clan,  which  is  a  form  of  segregate  breeding.  If  the  clan 
never  grows  beyond  the  powers  of  individual  recognition,  or  if  the 
numbers  never  become  so  great  as  to  impede  each  other  in  gaining 
sustenance,  there  will  be  but  little  occasion  for  segregation;  but 
multiplication  will  lead  to  subdivision.  Wherever  the  members  of  a 
species,  ranging  freely  over  a  given  area,  divide  up  into  separate  herds, 
flocks,  or  swarms,  of  which  the  members  produced  in  any  one  group 
breed  with  each  other  more  than  with  others,  there  we  have  social 
segregation. 

It  should  always  be  kept  in  mind  that  social  segregation  arises  at  a 
very  early  stage,  often  holding  apart  groups  but  very  slightly  differ- 
entiated; while  in  the  case  of  many  animals  the  sexual  instincts 
of  the  males  tend  to  break  up  these  minor  groups.  Though  the 
barriers  raised  by  social  instincts  are  often  broken  over,  their  in- 
fluence is  not  wholly  overcome,  and  in  many  instances  the  social 
segregation  becomes  more  and  more  pronounced,  till  in  time  decided 
sexual  segregation  comes  in  to  secure  and  strengthen  the  divergence. 

11.  Sexual  Segregation  is  Produced  by  the  Discriminative  Action  oj 
Sexual  Instincts. 

There  can  be  no  doubt  that  sexual  instincts  often  differ  in  such  a 
way  as  to  produce  segregation.  But  how  shall  we  account  for  these 
differences?  In  the  case  of  social  segregation  there  is  no  difficulty, 
for  it  seems  to  be,  like  migration,  due  to  a  constant  instinct,  always 
tending  to  segregation.  We  also  see  that  an  endowment  which  pre- 
vents the  destruction  of  the  species  through  the  complete  isolation  of 
individuals,  and  which  cooperates  with  migrational  instincts  in  secur- 
ing dispersal  without  extinction,  may  be  perfected  by  the  accumulat- 
ing effects  of  its  own  action.  And  is  there  any  greater  difficulty  in 
accounting  for  the  law  that  regulates  sexual  instincts?  If  it  can  be 
shown  that  vigor  and  variation,  the  conditions  on  which  adaptation 
depends,  are  in  their  turn  dependent  on  some  degree  of  crossing,  there 
will  be  no  difficulty  in  attributing  the  development  of  an  instinct 
that  secures  the  crossing  to  the  selection  of  the  individuals  that 
possess  it  in  even  a  small  degree.  On  the  other  hand,  whenever  there 
arises  a  variety  that  can  maintain  itself  by  crossing  within  the  same 


*  Numerals  are  used  to  designate  causes  of  segregation  not  depending  on  human 
purpose.     Of  these  nine  were  mentioned  in  the  section  on  environal  segregation. 


SEXUAL  SEGREGATION.  l6l 

variety,  any  variation  of  instinct  that  tends  to  segregation  will  be 
preserved  by  the  segregation.  It  needs  no  experiments  to  prove  that 
if  the  members  of  a  species  are  impelled  to  consort  only  with  the  mem- 
bers of  other  species,  they  will  either  fail  to  leave  offspring  or  their 
offspring  will  fail  to  inherit  the  characteristics  of  the  species.  The 
same  is  true  concerning  the  continuance  of  a  variety  that  is  not  some- 
how segregated.  The  power  of  variation  on  the  one  hand,  and  the 
power  of  divergent  accumulation  of  variations  on  the  other  hand,  are 
prime  necessities  for  creatures  that  are  wresting  a  living  from  a  vast 
and  complex  environment ;  and  the  former  is  secured  by  the  advan- 
tage over  rivals  possessed  by  the  variations  that  favor  crossing,  and 
the  latter  by  the  better  escape  from  the  swamping  effect,  and  some- 
times from  the  competition  of  certain  rivals,  secured  by  the  more 
segregative  variations.  We  must,  therefore,  believe  that  whenever 
in  the  history  of  an  organism  there  arise  segregative  variations  which 
are  able  to  secure  sufficient  sustentation  and  propagation  to  continue 
the  species,  the  segregative  quality  of  the  forms  thus  endowed  will  be 
preserved  and  accumulated  through  the  self-accumulated  effect  of  the 
segregative  endowments. 

It  is  probable  that  in  many  of  the  higher  vertebrates  sexual  in- 
stincts tend  to  bring  together  those  of  somewhat  divergent'  character, 
but  the  difference  preferred  is  within  very  narrow  limits ;  and  beyond 
those  limits  it  may  be  said  that  the  general  law  for  sexual  attraction 
is  that  it  varies  inversely  as  the  difference  in  the  characters  of  the  races 
represented,  if  not  inversely  as  some  power  of  such  difference.  The 
action  of  such  a  law  is  necessarily  segregative  whenever  the  diver- 
gence has,  through  other  causes,  passed  beyond  the  limit  of  higher 
attraction.  Before  sexual  segregation  can  arise,  there  must  arise 
distinctive  characteristics  by  means  of  which  the  members  of  any 
section  may  discriminate  between  those  of  their  own  and  other 
sections.  If  there  are  no  constant  characteristics  there  can  be  no 
constant  aversion  between  members  of  different  groups,  no  constant 
preference  of  those  of  one's  own  group.  From  this  it  follows  that 
before  sexual  segregation  can  arise,  some  form  of  segregation  that 
is  not  dependent  on  distinct  characteristics  must  have  produced 
the  divergence  on  which  the  sexual  segregation  depends.  Such 
forms  are  local,  social,  and  some  kinds  of  industrial  segregation. 
When  varieties  have  arisen  through  these  causes  it  often  happens  that 
sexual  segregation  comes  in  and  perpetuates  the  segregation  which  the 
initial  causes  can  no  longer  sustain.  As  long  as  the  groups  are  held 
apart  by  divergent  sexual  instincts,  it  is  evident  that  divergent  forms 
of  sexual  selection  are  almost  sure  to  arise,  leading  to  a  further  ac- 
cumulation of  the  divergence  initiated  by  the  previous  causes. 


1 62  APPENDIX   I — DIVERGENT   EVOLUTION. 

If  there  is  any  persistent  cause  by  which  local  and  social  groups  are 
broken  up  and  promiscuously  intermingled  before  recognizable  char- 
acters are  gained,  the  entrance  of  sexual  segregation  will  be  prevented. 
I  therefore  conclude  that  the  chief  influence  of  this  latter  factor  is 
found  in  its  prolonging  and  fortifying  the  separate  breeding  of  varie- 
ties that  have  arisen  under  local,  social,  or  industrial  segregation,  and 
in  thus  continuing  the  necessary  condition  for  the  development  of 
increasingly  divergent  forms  of  intensive  segregation,  under  which  the 
organism  passes  by  the  laws  of  its  own  vital  activity  when  dealing 
with  a  complex  environment  in  groups  that  never  cross. 

12.  Germinal  Segregation  is  Caused  by  the  Propagation  of  the  Species  by  means  of 

Seeds  or  Germs,  any  one  of  which,  when  developed,  forms  a  community  so 
related  that  the  members  breed  with  each  other  more  frequently  than  with  the 
members  of  other  communities. 

If  the  constitution  of  any  species  is  such  that  the  ovules  produced 
from  one  seed  are  more  likely  to  be  reached  and  fertilized  by  pollen 
produced  from  the  same  seed  than  by  pollen  produced  from  any  other 
one  seed,  then  germinal  segregation  is  the  result. 

In  order  to  secure  this  kind  of  segregation  it  is  not  necessary  that 
the  flowers  fertilized  by  pollen  from  the  same  plant  should  be  more 
fertile  or  the  seeds  capable  of  producing  more  vigorous  plants  than 
the  flowers  fertilized  by  pollen  from  another  plant.  All  that  is  re- 
quired is  that  the  seeds  produced  by  each  individual  plant  shall  be 
fertilized  by  the  pollen  of  the  same  plant. 

This  form  of  segregation  is  closely  related  to  local  segregation  on 
one  side  and  to  social  segregation  on  the  other.  It,  however,  differs 
from  the  former  in  that  it  does  not  depend  on  migration  or  trans- 
portation, and  from  the  latter  in  that  it  does  not  depend  on  social 
instincts. 

13.  Floral  Segregation  is  Segregation  arising  from  the  Closest  Form  of  Self-fertiliza- 

tion, namely,  of  the  Ovules  of  a  Flower  by  Pollen  from  the  same  Flower. 

Some  plants  that  in  their  native  haunts  are  frequently  crossed  by 
the  visits  of  insects  depend  entirely  on  self-fertilization  when  trans- 
ported to  other  countries  where  no  insect  is  found  to  perform  the  same 
service  for  them.  The  common  pea  {Pisum  sativum)  is  an  example 
of  a  species  that  does  not  fail  of  propagating  in  England,  though  Dar- 
win found  that  it  was  very  rarely  visited  by  insects  that  were  capable 
of  carrying  the  pollen,  and  the  pollen  is  not  carried  by  the  wind.* 
Darwin  also  mentions  Ophrys  apifera  as  an  orchid  which  "has  almost 
certainly  been  propagated  in  a  state  of  nature  for  thousands  of  gen- 
erations without  having  been  once  intercrossed,  "f 


*  Cross  and  Self  Fertilization  in  the  Vegetable  Kingdom,  p.  i6i.       f  Ibid.,  p.  439 


IMPREGNATIONAL  SEGREGATIOJJ.  1 63 

GENERAL   OBSERVATIONS  ON  GERMINAL  AND   FLORAL  SEGREGATION. 

A  fact  of  great  importance  in  its  bearing  on  the  origin  of  varieties 
should  be  here  noted.  Any  variation,  arising  as  a  so-called  sport,  in 
any  group  of  plants  where  either  of  these  principles  is  acting  strongly, 
will  be  restrained  from  crossing,  and  will  be  preserved  except  in  so  far 
as  reversion  takes  place.  Now,  there  is  always  a  possibility  that  some 
of  the  segregating  branches  of  descent  will  not  revert,  and  that, 
through  the  special  character  which  they  possess  in  common,  they  will 
some  time  secure  the  services  of  some  insect  that  will  give  them  the 
benefit  of  cross-fertilization  with  each  other  without  crossing  with 
other  varieties.  The  power  of  attaining  new  adaptations  may  be 
favored  by  self-fertilization  occasionally  interrupted  by  interbreeding 
with  individuals  of  another  stock ;  for  the  latter  is  favorable  as  intro- 
ducing vigor  and  variation,  and  the  former  as  giving  opportimity  for 
the  accumulation  of  variations. 

These  two  methods  of  propagation  are  so  far  removed  from  those 
found  in  the  majority  of  species  that  it  may  be  wise  to  consider  any 
transformation  arising  under  such  conditions  as  belonging  to  a 
separate  department  of  the  process  of  evolution.  Organisms  that  are 
self-fertilized  in  all  their  generations  seem  to  stand  in  nearer  relation 
to  species  entirely  without  the  power  of  sexual  propagation  than  to 
species  in  which  cross-fertilization  is  the  usual  method  of  propagation. 
(b)  Impregnational  Segregation. 

Impregnational  segregation  is  due  to  the  different  relations  in  which 
the  descendants  of  one  original  stock  stand  to  each  other  in  regard 
to  the  possibility  of  their  producing  fertile,  vigorous,  and  fully  adapted 
offspring  when  they  consort  together. 

In  order  that  impregnational  segregation  should  be  established  and 
perpetuated,  it  is  necessary,  first,  that  variation  should  arise,  from 
which  it  results  that  those  of  one  kind  are  capable  of  producing  vig- 
orous, adapted,'and  fertile  offspring  in  greater  numbers  when  breeding 
with  each  other  than  when  breeding  with  other  kinds ;  second,  that 
mutually  compatible  forms  should  be  so  brought  together  as  to  insure 
propagation  through  a  series  of  generations.  In  order  to  secure  this 
second  condition,  it  is  necessary  that,  in  the  case  of  plants,  there 
should  be  some  degree  of  local,  germinal,  or  floral  segregation,  and,  in 
the  case  of  animals  that  pair,  either  pronounced  local  segregation  or 
partial  local  segregation,  supplemented  by  social  or  sexual  segregation. 
The  action  of  the  different  forms  of  impregnational  segregation  I  call 
negative  segregation,  for  they  rest  on  incompatibilities  interfering  with 
mixed  unions  or  allowing  of  no  offspring,  or  of  but  few  or  inferior 
offspring,  as  the  result  of  mixed  unions,  and,  unaided  by  positive  seg- 


164  APPENDIX  I — DIVERGENT   EVOLUTION. 

regation,  can  do  nothing  toward  bringing  creatures  together  accord- 
ing to  their  compatibiHties.  The  forms  of  segregation  that  place  or 
draw  together  creatures  of  Hke  innate  characters  I  call  forms  of  posi- 
tive segregation. 

Of  each  form  of  segregation  which  we  have  up  to  this  point  con- 
sidered, the  segregating  cause  has  been  one  that  distributes  individuals 
of  the  same  species  in  groups  between  which  free  intergeneration  is 
checked;  while  the  propagation  of  the  different  groups  depends  sim- 
ply on  the  original  capacity  for  intergenerating  common  to  all  the 
members  of  the  species.  The  intercrossing  has  been  limited  not  by 
the  capacity  but  by  the  opportunity  and  inclination  of  the  members. 
Coming  now  to  cases  in  which  complete  lack  of  capacity  for  fruitful 
crossing  is  the  cause  that  prevents  the  production  of  mongrels,  we  find 
a  dependence  of  a  very  different  kind ;  for  to  insure  the  propagation  of 
the  different  groups  it  is  not  enough  that  the  general  opportunity  for 
the  members  of  the  species  to  meet  and  consort  remains  unimpaired. 
There  must  be  some  additional  segregating  influence  bringing  the 
members  together  in  groups  corresponding  to  their  segregate  capacity, 
or  they  will  fail  of  being  propagated. 

The  form  of  impregnational  segregation  which  I  call  prepotential 
segregation  is  due  to  the  prepotency  of  the  pollen  of  a  species  or  variety 
on  the  stigma  of  the  same  species  or  variety,  and  complete  potential 
segregation  is  due  to  the  potency  of  the  pollen  of  the  same  species,  with 
the  complete  impotence  of  the  foreign  pollen.  When  allied  species  of 
plants  are  promiscuously  distributed  over  the  same  districts,  and 
flowering  at  the  same  time,  prepotency  of  this  kind,  aided  by  the  free  dis- 
tribution of  the  pollen  by  the  wind,  is  one  of  the  most  direct  and  efhcient 
causes  of  segregate  breeding.  The  same  must  be  true  of  varieties 
similarly  distributed  whenever  this  character  begins  to  affect  them. 
In  the  case,  however,  of  dioecious  plants  and  of  plants  whose  ovules 
are  incapable  of  being  impregnated  by  pollen  from  the  same  plant,  no 
single  plant  can  propagate  the  species.  If,  therefore,  the  individuals 
so  varying  as  to  be  prepotent  with  each  other  are  very  few,  and  are 
evenly  distributed  amongst  a  vast  number  of  the  original  form,  the 
probability  is  that  they  will  fail  of  being  segregated  through  failing 
to  receive  any  of  the  prepotent  pollen.  It  is  thus  apparent  that  when 
the  mutually  prepotent  form  is  represented  by  comparatively  few  indi- 
viduals, their  propagation  without  crossing  will  depend  on  their  being 
self -fertile  and  subject  to  germinal  or  floral  segregation,  or  on  their 
being  brought  together  by  some  other  form  of  positive  segregation. 

When  a  considerable  number  of  species  of  plants  are  commingled 
and  are  flowering  at   the  same  time,  their  separate  propagation  is 


DIMENSIONAIv    AND  STRUCTURAL   SEGREGATION.  165 

preserved,  in  no  small  degree,  by  the  prepotential  segregation  of  those 
that  are  most  nearly  allied  and  by  the  complete  potential  segregation 
of  those  that  belong  to  different  families,  orders,  and  classes.  The 
same  principle  must  come  in  to  prevent  the  crossing  of  different  spe- 
cies, genera,  families,  and  orders  of  animals  whose  fertilizing  elements 
are  distributed  in  the  water.  When  aided  by  this  free  distribution  the 
combined  effect  is  that  of  positive  as  well  as  negative  segregation ;  for 
the  free  distribution  of  the  fertilizing  element,  with  the  superior  affinity 
of  the  two  sexual  elements  that  are  mutually  prepotent,  secures  the 
interbreeding  of  the  species  or  variety  producing  the  mutually  prepo- 
tent elements. 

Impregnational  segregation  generally  exists  between  the  different 
species  of  the  same  genus,  almost  always  between  species  of  different 
genera,  and  always  between  species  of  different  families,  orders, 
classes,  and  all  groups  of  higher  grade.  And  in  all  these  cases  it  is 
associated  with  other  forms  of  segregation,  and  when  once  complete 
the  groups  affected  never  coalesce.  Though  complete  mutual  ster- 
ility never  gives  place  to  complete  mutual  fertility,  in  every  case 
where  the  descendants  of  the  same  stock  have  developed  into  different 
classes  or  orders,  and  in  most  cases  where  they  have  developed  into 
different  families  or  genera,  the  reverse  process  has  taken  place,  and 
complete  mutual  fertility  has  given  place  to  complete  mutual  sterility. 

Under  impregnational  segregation  I  distinguish  dimensional  segre- 
gation, structural  segregation,  potential  segregation,  segregate  fecun- 
dity, segregate  vigor,  segregate  adaptation,  segregate  freedom  from 
competitio.n,  and  segregate  escape  from  enemies. 

14.  Dimensional  Segregation  (or  Segregative  Size)  is  caused  by  Incompatibility 

in  Size  or  Dimensions  of  the  Individuals  of  the  Different  Breeds. 

As  familiar  illustrations  of  this  form  of  segregation,  I  may  mention 
the  following:  The  largest  and  smallest  varieties  of  the  ass  may  run 
in  the  same  pasture  without  any  chance  of  crossing.  I  have  also  kept 
Japanese  bantam  fowls  in  the  same  yard  with  other  breeds  without 
any  crossing.  In  many  other  species  individuals  of  extreme  diver- 
gence in  size  are  incapable  of  interbreeding. 

15.  Structural  Segregation  {or  Segregative  Structure)  is  Caused  by  Lack  of 
Correlation  in  the  Size  of  Different  Organs  and  by  other  Incompatibilities 
of  Structure. 

Darwin  suggests  that  the  impossibility  of  a  cross  between  certain 
species  may  be  due  to  a  lack  of  correspondence  in  length  of  the  pollen 
tubes  and  pistils.  Such  a  lack  of  harmony  would  perhaps  account 
for  difference  of  fertility  in  reciprocal  crosses,  according  as  the  male  is 
of  the  one  variety  or  of  the  other. 


1 66  APPENDIX   I — DIVERGENT  EVOLUTION. 

Segregative  structure  does  not  usually  arise  till  other  forms  of  segre- 
gation have  become  so  well  established  that  difference  of  structure 
does  not  make  any  essential  difference  in  the  amount  of  intergenera- 
tion.  It  is  not,  however,  impossible  that  species  that  would  otherwise 
freely  cross  are  thus  held  apart.  In  Broca's  work  on  "Human 
Hybridity"*  there  is  a  passage  quoted  from  Prof.  Serres  showing 
that  it  is  very  possible  that  this  form  of  incompatibility  may  exist 
between  certain  races  of  men. 

16.  Potential  Segregation  {or  Segregative  Potency)  in  its  Two  Forms,  Complete 
Potential  Segregation  and  Prepotential  Segregation. 

(i)  Nature  of  the  Principle. — It  is  caused  by  the  greater  rapidity 
and  efficiency  with  which  the  sexual  elements  of  the  same  species, 
race,  or  individual  combine.  Complete  potential  segregation  is 
caused  by  the  mutual  impotence  of  the  contrasted  forms,  as  is  always 
the  case  between  different  orders  and  classes ;  and  prepotential  segre- 
gation is  caused  by  the  superior  influence  of  the  fertilizing  element 
from  the  same  species,  race,  or  individual,  as  contrasted  with  that 
from  any  other  species,  race,  or  individual,  when  both  reach  the  same 
ovum  at  the  same  time,  or  sometimes  when  the  prepotent  element 
comes  many  hours  after  the  other.  That  propagation  may  result 
compatible  elements  must  meet. 

When  pollen  from  a  contrasted  genus,  order,  or  class  has  no  more 
effect  than  inorganic  dust,  it  seems  appropriate  that  we  should  call 
the  result  complete  potential  segregation  rather  than  prepotential 
segregation,  which  implies  that  the  foreign  as  well  as  the  home  pollen 
is  capable  of  producing  impregnation.  Prepotential  segregation  may 
be  considered  the  initial  form  of  potential  segregation.  The  principle 
is  fundamentally  one,  though  it  will  be  convenient  to  retain  both 
names. 

The  importance  of  this  principle  in  producing  and  preserving  the 
diversities  of  the  vegetable  kingdom  can  hardly  be  overstated.  If 
pollen  of  every  kind  were  equally  potent  on  every  stigma,  what  would 
the  result  be?  What  distinctions  would  remain?  And  if  potential 
segregation  is  necessary  for  the  preservation  of  distinctions,  is  it  not 
equally  necessary  for  their  production  ?  Amongst  water  animals  that 
do  not  pair,  the  same  principle  of  segregation  is  probably  of  equal 
importance.  Concerning  this  form  of  segregation  many  questions  of 
great  interest  suggest  themselves,  answers  to  which  are  not  found  in 
any  investigations  with  which  I  am  acquainted. 


*  English  translation,  published  by  the  Anthropological  Society  of  London,  p.  28. 


POTENTIAL  SEGREGATION.  167 

Some  of  these  questions  are  as  follows : 

(2)  Points  needing  investigation. — First.  Are  there  many  cases  of 
prepotential  as  well  as  of  complete  potential  segregation  between  dif- 
ferent forms  of  water  animals? 

Second.  Is  prepotential  segregation  always  accompanied  by  segre- 
gate fecundity  and  segregate  vigor? 

Third.  If  not  always  associated,  which  of  the  three  principles 
first  appears?     And  what  are  their  relations  to  each  other? 

Fourth.  When  allied  organisms  are  separated  by  complete  environal 
segregation,  are  they  less  liable  to  be  separated  by  these  three  prin- 
ciples? 

Darwin  has  in  several  places  referred  to  the  influence  of  prepotency 
in  pollen,  and  in  two  places  I  have  found  reference  to  the  form  of  pre- 
potency that  produces  segregation ;  but  I  find  no  intimation  that  he 
regarded  this  or  any  other  form  of  segregation  as  a  cause  of  divergent 
evolution.  The  effect  of  prepotency  in  pollen  from  another  plant  in 
preventing  self-fertilization  is  considered  in  the  tenth  chapter  of  his 
work  on  "Cross-  and  Self-fertilization  in  the  Vegetable  Kingdom,"  pp. 
391-400.  Some  very  remarkable  observations  concerning  the  pre- 
potency of  pollen  from  another  variety  than  that  in  which  the  stigma 
grows  are  recorded  in  the  same  chapter,  but  no  reference  is  there 
made  to  the  effect  that  must  be  produced  when  the  pollen  of  each 
variety  is  prepotent  on  the  stigma  of  the  same  variety. 

In  Chapter  XVI  of  "Variation  under  Domestication  "  it  is  suggested 
that  prepotency  of  this  kind  might  be  a  cause  of  different  varieties  of 
double  hollyhocks  reproducing  themselves  truly  when  growing  in  one 
bed,  though  there  was  another  cause  to  which  the  freedom  from 
crossing  in  this  case  has  been  attributed.  Again,  in  Chapter  VIII 
of  the  fifth  edition  of  "The  Origin  of  Species,"  in  the  section  on  "The 
Origin  and  Causes  of  Sterility,"  Darwin,  while  maintaining  that  the 
mutual  sterility  of  species  is  not  due  to  natural  selection,  refers  to 
prepotency  of  the  kind  we  are  now  considering  as  a  quality  which, 
occurring  in  ever  so  slight  a  degree,  would  prevent  deterioration  of 
character,  and  which  would,  therefore,  be  an  advantage  to  a  species 
in  the  process  of  formation,  and  accordingly  subject  to  accumulation 
through  natural  selection.  In  order  to  construct  a  possible  theory 
for  the  introduction  of  sterility  between  allied  species  by  means  of 
natural  selection,  he  finds  it  necessary  simply  to  add  the  supposition 
that  sterility  is  directly  caused  by  this  prepotency.  He,  however,  for 
several  reasons,  concludes  that  there  is  no  such  dependence  of  mutual 
sterility  on  the  process  of  natural  selection.  Concerning  the  pre- 
potency he  makes  no  reservation,  and  I  accordingly  judge  that  he 


1 68  APPENDIX  I — DIVERGENT  EVOLUTION. 

continued  to  regard  it  as  strengthened  and  developed  through  the 
action  of  natural  selection.* 

(3)  Reasons  for  believing  that  potential  segregation  can  not  be  accti- 
mulated  by  natural  selection. — Concerning  this  last  point  I  wish  to  give 
reasons  for  a  different  opinion.  I  believe  that  qualities  simply  produc- 
ing segregation  can  never  be  accumulated  by  natural  selection,  for — 

First.  When  separate  generation  comes  in  between  two  sections 
of  a  species  they  cease  to  be  one  aggregate,  subject  to  modification 
through  the  elimination  of  certain  parts.  Both  will  be  subject  to  sim- 
ilar forms  of  natural  selection  only  so  long  as  the  circumstances  of 
both  and  the  variations  of  both  are  nearly  the  same,  but  they  will  no 
longer  be  the  members  of  one  body  between  which  the  selecting  pro- 
cess is  carried  out.  On  the  contrary,  if  they  occupy  the  same  district 
each  group  will  stand  in  the  relation  of  environment  to  the  other,  mod- 
ifying it,  and  being  modified  by  it,  without  mutually  sharing  in  the 
same  modification. 

Second.  Though  one  may  exterminate  the  other,  the  change  that 
comes  to  the  successful  group  through  the  contest  is  not  due  to  its 
superiority  over  the  other,  but  to  the  superioritv  of  some  of  its  own 
members  over  others. 

Third.  When  any  segregate  form  begins  to  arise  we  can  not  attribute 
its  success  to  the  advantage  of  isolation,  for  it  is  not  the  success,  but 
the  separateness  of  the  success,  that  is  due  to  the  isolation. 

Fourth.  The  power  of  migration,  or  any  other  power  directly  re- 
lated to  the  environment,  may  be  accumulated  by  natural  selection, 
and  afterward  lead  to  segregation,  but,  according  to  my  method  of 
judging,  the  advantage  of  segregation  over  intergeneration  is  not  the 
cause  of  the  preservation  of  forms  endowed  with  segregative  qualities, 
for  they  will  certainly  be  preserved  as  long  as  they  are  able  to  win  a 
bare  existence,  which  is  often  a  lower  grade  of  success  than  the  one 
from  which  they  are  passing. 

(4)  How  shall  we  explain  the  accumulation  of  potential  segregation? — 
But  if  the  accumulation  of  prepotential  segregation  is  not  due  to  nat- 
ural selection,  how  shall  we  explain  it?  The  divergence  of  a  group 
can  not  take  place  without  its  being  segregated  from  the  original  stock 
as  well  as  from  other  types ;  and  the  potency  of  the  sexual  elements  of 
the  new  group  will  be  maintained  in  their  relations  to  each  other  by 
some  form  of  reflexive  selection ;  but  as  there  can  be  no  reflexive  selec- 
tion between  the  segregated  groups,  the  potency  of  the  elements  for 
crossing  outside  of  the  group  will  in  time  be  impaired ;  and  then  we 


*  Since  my  comments  on  this  passage  were  written  I  have  discovered  that  Dar 
win  has  omitted  it  from  the  sixth  edition. 


ACCUMULATION  OF   POTlvNTlAL  SliGRCGATlON.  1 69 

shall  have  prepotency  of  each  group  within  the  circle  of  its  own  group. 
This  process  may  take  place  when  a  group  is  protected  by  complete 
isolation,  however  produced.  Let  us  next  consider  a  case  in  which  a 
small  group  partially  protected  from  mixture  with  the  original  type 
by  incomplete  local  and  industrial  segregation  produces  a  variation 
whose  ovules  are  more  readily  fertilized  by  pollen  from  the  same 
group  than  by  pollen  from  the  original  type.  Is  it  not  evident  that 
this  variation  will  gain  with  each  generation  an  increasing  prominence 
in  the  new  group  that  maintains  somewhat  new  methods  of  dealing 
with  the  environment  in  its  partially  isolated  habitat?  This  will  be 
so,  first,  because  variations  possessing  but  little  or  no  prepotency  with 
their  own  group  will  eventually  coalesce  with  the  original  stock,  and 
especially  will  this  be  the  case  if  the  new  group  becomes  somewhat 
numerous  and  passes  beyond  the  limits  of  its  narrow  habitat  into 
districts  where  the  original  type  abounds ;  and,  second,  because  vari- 
ations possessing  the  prepotency  with  their  own  group  in  a  superior 
degree  will  remain  distinct,  breeding  with  each  other,  and  their  de- 
scendants will  become  still  more  segregate  and  still  more  perma- 
nently divergent.  Of  the  law  of  accumulation  of  segregative  endow- 
ments, we  may  say  that  as  the  descendants  of  the  best  fitted  necessarily 
generate  with  each  other  and  produce  those  still  better  fitted,  so  the  de- 
scendants of  those  possessing  the  most  segregative  endowments  necessarily 
generate  with  each  other  and  produce  those  that  are  still  more  segregate. 
It  will,  however,  soon  be  shown  that  unless  the  reproduction  and 
power  of  survival  is  greater  for  the  pure  segregate  forms  than  for 
the  mixed  forms,  the  proportion  of  pure  forms  to  mixed  forms  will 
decrease  in  each  generation. 

It  is  evident  that  when  either  segregate  potency  or  segregate  pre- 
potency is  associated  with  the  free  distribution  of  the  fertilizing  ele- 
ment by  wind  or  water,  the  combined  effect  must  be  in  the  former  case 
complete,  and  in  the  latter  case  partial,  positive  segregation,  for  the 
breeding  together  of  compatible  forms  is  thereby  secured. 

It  may  at  first  appear  that  a  slight  degree  of  segregate  prepotence 
will  prevent  crossing  as  effectually  as  a  higher  degree,  but  further 
reflection  will  show  that  the  efficiency  of  the  prevention  will  vary  in 
direct  proportion  with  the  length  of  time  over  which  the  prepotent 
pollen  is  able  to  show  its  prepotence,  and  this  will  allow  of  innumer- 
able grades.  If,  in  the  case  of  certain  individuals,  the  prepotency  is 
measured  by  about  twenty  minutes,  while  with  other  individuals  it 
enables  the  pollen  of  the  same  variety  to  prevail  though  reaching  the 
stigma  an  hour  after  the  pollen  of  another  variety  has  been  applied, 
the  difference  in  the  degree  of  segregation  will  be  sufficient  to  make 
the  persistence  of  the  latter  much  more  probable  than  that  of  the 


I70  APPENDIX  I — DIVERGENT  EVOLUTION. 

former.  This  form  of  segregation  is  evidently  one  of  the  important 
causes  preventing  the  free  crossing  of  different  species  of  plants.  It 
probably  has  but  little  influence  on  terrestrial  animals ;  but  how  far 
it  is  the  cause  of  segregation  among  aquatic  animals  is  a  question  of  no 
small  interest,  concerning  which  I  have  but  small  means  for  judging. 
I  have,  however,  no  hesitation  in  predicting  that,  unless  we  make  the 
presence  of  this  segregative  quality  the  occasion  for  insisting  that  the 
forms  so  affected  belong  to  different  species,  we  shall  find  that  amongst 
plants  the  varieties  of  the  same  species  are  often  more  or  less  separated 
from  each  other  in  this  way.  I  do  not  know  of  any  experiments  that 
have  been  directed  toward  the  determining  of  this  point ;  but  on  the 
general  principle  that  race  distinctions  are  the  initial  forms  under 
which  specific  differences  present  themselves,  I  can  have  no  doubt 
that  feeble  prepotence  precedes  that  which  is  more  pronounced,  and 
that  part  of  this  divergence  in  many  cases  takes  place,  while  the  diver- 
gent branches  may  be  properly  classed  as  varieties.  Another  reason 
for  believing  that  prepotential  segregation  will  be  found  on  further 
investigation  to  exist  in  some  cases  between  varieties  is  the  constancy 
with  which,  in  the  case  of  species,  this  character  is  associated  with 
segregate  fecundity  and  segregate  vigor,  which  we  know  are  sometimes 
characteristics  of  varieties  in  their  relation  to  each  other. 

17,  18.  Segregate  Fecundity  and  Segregate  Vigor. 
By  segregate  fecundity  I  mean  neither  segregation  produced  by 
fecundity  nor  fecundity  produced  by  segregation,  but  the  relation  in 
which  species  or  varieties  stand  to  each  other  when  intergeneration 
of  members  of  the  same  species  or  variety  results  in  higher  fertility 
than  the  crossing  of  different  species  or  varieties.  In  like  manner 
segregate  vigor  is  the  relation  in  which  species  or  varieties  stand  to 
each  other  when  the  intergeneration  of  members  of  the  same  species 
or  variety  produces  offspring  more  vigorous  than  those  produced  by 
crossing  with  other  species  or  varieties.  Integrate  fecundity  and 
integrate  vigor  are  the  terms  by  which  I  indicate  the  relation  to  each 
other  of  forms  in  which  the  highest  fertility  and  vigor  are  produced  by 
crossing,  and  not  by  independent  generation. 

19.  Segregate  Adaptation* 
Segregate  adaptation  is  the  relation  in  which  species  or  varieties 
stand  to  each  other  when  the  intergeneration  of  individuals  of  the 
same  species  or  variety  produces  offspring  better  adapted  than  the 


*  This  and  the  following  paragraph  were  not  in  the  paper  as  first  published, 
though  the  advantage  of  escape  from  severe  competition  with  members  of  the 
same  species  was  set  forth  in  the  paragraph  entitled  "  Competitive  disruption." 


SEGREGATE  FECUNDITY,   VIGOR,  AND  ADAPTATION.  171 

offspring  produced  by  crossing  with  other  species  or  varieties.  Nat- 
ural selection  is  the  survival  of  the  best  adapted  of  the  variations  that 
remain  and  breed  with  the  stock  under  consideration,  but  it  takes  no 
cognizance  of  the  fitness  or  lack  of  fitness  of  individuals  or  a  race  that 
separate  themselves  from  the  intergenerating  mass.  The  different 
grades  of  fitness  for  their  new  life  found  among  the  individuals  that 
form  the  new  intergenerating  group  will  be  the  ground  for  divergent 
natural  selection  in  the  new  group ;  but  they  will  not  affect  the  type 
of  the  original  stock.  Now,  whenever  the  conditions  and  aptitudes  of 
the  two  groups  are  so  different  that  the  offspring  of  cross-unions  are 
less  fitted  for  life  under  either  set  of  conditions  than  is  either  group  of 
the  pure-breeds  for  its  own  peculiar  life,  we  shall  have  a  new  principle, 
different  in  its  effects  from  natural  selection.  This  I  call  segregate 
adaptation.  Natural  selection  is  the  survival  of  the  fittest  that  inter- 
generate  ;  segregate  adaptation  is  the  superior  fitness  and  survival  of 
the  offspring  produced  by  segregate  generation. 

20,  21 .  Segregate  Freedom  from  Competition  and  Segregate  Escape  from  Enemies. 

Segregative  endowments  may  be  necessary  to  the  enjoyment  of  cer- 
tain advantages  which  are  gained  not  by  superior  adaptation  to  the 
environment,  but  by  endowments  that  set  them  in  a  position  where 
competitors  and  enemies  are  as  yet  few.  These  two  principles  I  have 
called  segregate  freedom  from  competition  and  segregate  escape  from 
enemies.  Segregate  freedom  from  competition  or  segregate  access  to 
unused  resources  results  when  the  pure  offspring  have  freer  access  to 
unused  resources  than  do  the  cross-breeds  or  the  original  stock. 
Segregate  escape  from  enemies  (an  advantage  often  of  equal  import- 
ance with  that  just  mentioned)  arises  whenever  the  pure  offspring 
of  a  divergent  variety  are  able  to  occupy  a  position  freer  from  enemies 
than  that  occupied  by  the  original  stock. 

(c)  Institutional  Segregation. 

Institutional  segregation  is  the  reflexive  form  of  rational  segrega- 
tion. It  is  produced  by  the  rational  purposes  of  man  embodied  in 
institutions  that  prevent  free  intergeneration  between  the  different 
parts  of  the  same  race. 

As  the  principal  object  of  the  present  paper  is  to  call  attention  to 
the  causes  of  segregation  acting  independently  of  effort  and  contriv- 
ance directed  by  man  to  that  end,  it  will  be  sufficient  to  enumerate 
some  of  the  more  prominent  forms  under  which  institutional  segrega- 
tion presents  itself,  noting  that  some  of  these  influences  come  in  as 


172  APPENDIX   I — DIVERGENT  EVOLUTION. 

supplemental  to  the  laws  of  segregation  already  discussed,  simply 
reinforcing  by  artificial  barriers  the  segregations  that  have  their  orig- 
inal basis  in  nature.  The  chief  forms  to  be  enumerated  are  national, 
linguistic,  caste,  penal,  sanitary,  and  educational  segregation.* 

CoNci/UDiNG  Remarks. 

1.  Impregnational  Segregation  a  Cause  of  Divergence  in  both  its  Earlier 
and  Later  Stages. 

The  negative  forms  of  segregation  would  tend  to  produce  extinc- 
tion if  they  were  not  associated  with  the  positive  forms  of  segregation. 
But  in  the  case  of  organisms  whose  fertilizing  elements  are  dis- 
tributed by  wind  and  water,  the  qualities  that  produce  these  nega- 
tive forms  of  segregation  are  usually  accompanied  by  those  that 
produce  potential  segregation,  and  potential  segregation  cooperating 
with  this  free  distribution  results  in  positive  segregation.  But  even 
prepotential  segregation,  when  produced  by  mutual  incompatibility 
between  a  few  individuals  and  a  numerous  parent  stock,  depends  for 
its  continuance  and  development  on  some  degree  of  local,  germinal, 
or  floral  segregation,  partially  securing  the  intergeneration  of  the  few 
that  are  mutually  compatible.  On  the  one  hand,  impregnational 
segregation  depends  on  some  degree  of  local,  germinal,  or  floral  segre- 
gation which  is  a  constant  feature  in  most  species;  and,  on  the  other 
hand,  not  only  do  these  initial  forms  of  positive  segregation  fail  of 
producing  any  permanent  divergence  till  associated  with  impreg- 
national segregation,  but  the  more  effective  forms  of  positive  segrega- 
tion, such  as  industrial,  chronal,  fertilizational,  sexual,  and  social 
segregation,  often  depend  on  impregnational  segregation,  inasmuch 
as  the  divergence  of  endowments  which  produces  these  depends  on 
impregnational  segregation.  Moreover,  in  all  such  cases,  increasing 
degrees  of  diversity  in  the  forms  of  adaptation,  and  consequently  of 
diversity  in  the  forms  of  natural  selection,  must  also  depend  upon 
these  negative  factors,  which  in  their  turn  depend  on  the  weak,  initial 
forms  of  positive  segregation. 

Divergent  evolution  always  depends  on  some  degree  of  positive 
segregation,  but  not  always  on  negative  segregation.     Under  positive 


*  This  completes  the  classification  of  the  forms  of  isolation  which  are  here  pre- 
sented as  forms  of  demarcational  segregation.  It  is  probably  correct  to  say  that 
with  the  exception  of  transportational  and  geological  isolation,  and  perhaps  some 
cases  of  migrational  isolation,  all  the  forms  of  isolation  so  far  discovered  are,  from 
the  first,  more  or  less  discriminative,  and,  therefore,  segregative.  Moreover,  if 
transportational  or  geological  action  plants  an  isolated  colony  of  only  a  few  indi- 
viduals, the  average  type  of  the  original  stock  is  not  fully  represented  in  the  colony 
and,  therefore,  the  effect  is  more  or  less  segregative  from  the  beginning. 


SEXUAL  INCOMPATIBILITY.  1 73 

segregation  of  a  rigorous  form  (as,  for  example,  complete  geograph- 
ical segregation),  considerable  divergence  may  result  without  any 
sexual  incompatibility.  Darwin  has  shown,  by  careful  experiments, 
that  integrate  vigor  and  fecundity  is  the  relation  in  which  the  varieties 
of  one  species  often  stand  to  each  other.  This  fact  does  not,  how- 
ever, prove  that  the  more  strongly  divergent  forms,  called  species, 
which  are  prevented  from  coalescing  by  segregate  vigor  and  fecundity, 
did  not  acquire  some  degree  of  this  latter  character  before  any  perma- 
nent divergence  of  form  was  acquired.  Their  having  acquired  this 
segregating  characteristic  may  be  the  very  reason  why  their  forms  are 
now  so  decidedly  different,  for  without  it  they  would  have  been  s>val- 
lowed  up  by  the  incoming  waves  of  intergeneration.  Again,  we  must 
remember  that  forms  only  moderately  divergent  are  habitually 
classed  as  different  species  if  they  are  separated  by  segregate  vigor 
and  fecundity  (that  is,  by  some  degree  of  mutual  sterility),  unless 
observation  shows  that  they  are  of  common  descent.  These  two 
considerations  sufficiently  explain  why  the  varieties  of  one  species 
are  so  seldom  reported  as  mutually  infertile.  Notwithstanding  this, 
the  experiments  of  Gartner  and  of  Darwin  seem  to  show  that  seg- 
regate fecundity  and  vigor  may  arise  between  varieties  that  spring 
from  one  stock.  In  view  of  these  cases  we  must  believe  that  in 
the  formation  of  some,  if  not  many  species,  the  decisive  event 
with  which  permanent  divergence  of  allied  forms  commences  is  the 
intervention  of  segregate  fecundity  or  vigor  between  these  forms. 
Positive  segregation,  in  the  form  of  local,  germinal,  or  floral  segrega- 
tion, producing  only  transitory  divergences,  always  exists  between  the 
portions  of  a  species  that  has  many  members;  but  as  it  does  not 
directly  produce  the  negative  segregation  which  is,  in  such  cases,  the 
necessary  antecedent  of  permanent  divergence,  we  can  not,  in  accord- 
ance with  the  usage  of  language,  call  it  the  cause  of  the  permanent 
divergence.  Moreover,  though  it  may  be  in  accordance  with  ordinary 
language  to  call  the  negative  segregation,  which  is  the  immediate 
antecedent  of  the  permanent  divergence  the  cause  of  the  same,  it  will 
be  more  correct  to  call  the  coincidence  of  the  negative  and  positive 
segregations  the  cause,  and  still  more  accurate  to  say  that  the  whole 
range  of  vital  activities  (when  subjected  to  the  limitations  of  any 
sexual  incompatibility  that  corresponds  in  the  groups  it  separates  to 
some  previous  but  ineffectual  local,  germinal,  or  floral  segregation) 
will  produce  permanent  divergence. 

In  many  cases  not  only  is  the  entrance  of  impregnational  segrega- 
tion the  cause  of  the  commencement  of  permanent  divergence,  but  its 
continuance  is  the  cause  of  the  continuance  of  the  divergence.     The 


1 74  APPENDIX  I — DIVERGENT  EVOLUTION. 

clearest  illustration  of  this  is  found  in  the  case  of  plants  that  are  fer- 
tilized by  pollen  that  is  distributed  by  the  wind.  All  the  higher,  as 
well  as  the  lower,  groups  of  such  plants  would  rapidly  coalesce  if  each 
grain  of  pollen  was  capable  of  producing  fertilization,  with  equal  cer- 
tainty, promptness,  and  efficiency,  on  whatever  stigma  it  might  fall. 
We  may  also  be  sure  that  with  organisms  that  depend  upon  water  for 
the  distribution  of  their  fertilizing  elements,  impregnational  segrega- 
tion is  an  essential  factor  in  the  development  of  higher  as  well  as  of 
lower  taxonomic  groups. 

It  is  important  to  obser\'^e  that,  in  the  cases  under  consideration, 
the  inferior  fertility  or  vigor  resulting  from  the  crossing  of  the  incom- 
patible forms  is  as  truly  a  cause  of  divergence  as  the  inferior  oppor- 
tunity for  crossing  which  from  the  first  existed  between  the  members 
occupying  different  localities  or  between  flowers  growing  on  different 
trees  of  the  same  species.  The  former  has  been  called  negative  and 
the  latter  positive  segregation,  not  for  the  sake  of  distinguishing 
different  grades  of  efficiency,  but  for  the  sake  of  indicating  the  different 
methods  of  operation  in  the  two  classes  of  segregation. 

2.  Isolation  Usually  Somewhat  Discriminate,  and  therefore  Segregative, 
from  the  First. 

Of  the  twenty-one  natural  forms  of  isolation  enumerated  in  this 
paper,  there  are  only  two  that  are  usually  indiscriminate  in  their 
action.  These  are  transportational  segregation  and  geological  segre- 
gation. And  even  these  sometimes  become  discriminate  in  their 
action  through  the  fact  that  those  individuals  that  are  similarly 
endowed  are  liable  to  be  transported  in  the  same  way  and  to  the  same 
place,  or  to  escape  together  from  destruction  in  geological  disturb- 
ances. Again,  it  may  happen  that  by  gradual  subsidence  a  large 
island  will  be  divided  into  two  smaller  islands,  and  thus  certain 
species  inhabiting  the  original  island  may  be  indiscriminately  isolated. 
But  even  in  such  a  case,  unless  the  average  inheritable  character  of 
each  section  of  the  species  is  exactly  the  same  in  all  respects,  the  effect 
is  segregative  from  the  first.  If  one,  or  both,  of  the  sections  is  very 
small,  the  probability  of  exact  similarity  in  all  respects  entirely  dis- 
appears, unless  the  species  is  wanting  in  plasticity  and  variability. 

3.  Principles  Intensifying  Segregation. 

Besides  artificial  and  institutional  segregation,  which  depend  on 
the  rational  purpose  of  man,  we  have  now  considered  2 1  forms  of  seg- 
regation, resting  on  purely  natural  causes. 

At  some  other  time  I  shall  endeavor  to  present  the  natural  laws  that 
cooperate  in  intensifying  the  effects  produced  by  the  segregative 


PRINCIPLES   INTENSIFYING  SEGREGATION.  1 75 

causes  already  considered.  Segregation  is  not  simply  the  indepen- 
dent generation  of  different  sections  of  a  species,  but  the  independent 
generation  of  sections  that  differ.  Though  indiscriminate  isolation  of 
a  small  section  of  a  species  may  produce  an  initial  difference,  it  is 
evident  that  the  degrees  of  difference  may  be  greater  or  less,  and  that 
whatever  causes  a  greater  difference  in  two  sections  that  are  prevented 
from  intergenerating  will  also  be  a  cause  of  increased  segregation,  and 
may  be  classed  as  a  form  of  intensive  segregation. 

It  has  been  observed  that  some  of  the  causes  enumerated  in  this 
chapter  are  primariljr  separative,  and  that  no  one  of  those  that  are 
primarily  segregative  is  at  any  one  time  segregative  in  regard  to  many 
classes  of  characters.  As  several  forms  of  segregation  may  cooperate 
in  securing  a  given  division  of  a  species,  and  one  form  is  superimposed 
upon  another,  the  aggregate  effect  must  be  great;  but  we  easily 
perceive  that  it  may  be  indefinitely  enhanced  by  causes  producing 
increased  divergence  in  the  segregated  branches.  The  causes  which 
produce  monotypic  evolution  when  associated  with  intergeneration 
must  be  equally  effective  in  producing  polytypic  evolution  when  asso- 
ciated with  isolation  whether  in  its  separative  or  segregative  forms. 
But  the  discussion  of  intensive  segregation  must  be  reserved  for 
another  occasion. 

A  Lack  in  this  First  Classification  of  Segregative  Principles* 
The  classification  of  segregative  principles  here  given  does  not  draw  any  clear 
distinction  between  those  resting  upon  acquired  characters  and  habitudes  and 
those  resting  upon  innate  characters  and  aptitudes.  For  example,  industrial 
segregation  is  defined  as  "Segregation  arising  from  the  activities  by  which  the 
organism  protects  itself  against  adverse  influences  in  the  environment,  or  by 
which  it  finds  and  appropriates  special  resources  in  the  environment."  Now  it 
is  manifest  that  in  some  cases  the  differ'^nt  methods  of  using  the  environment  may 
be  determined  by  acquired  habitudes  rather  than  by  inherited  aptitudes,  and  the 
demarcation  thus  produced  will,  in  the  first  place,  be  habitudinal,  though  in  the 
end  it  may  result  in  racial  demarcation. 

The  interaction  between  the  principles  producing  racial  segregation  and  those 
producing  habitudinal  segregation  is  discussed  in  Chapter  V  (pp.  45-78). 

It  should  also  be  noted  that  since  this  paper  was  brought  before  the  Linnean 
Society,  isolation  has  come  into  general  use  for  designating  the  prevention  of  free 
crossing,  by  which  the  demarcation  of  racial  groups  is  determined.  This  leaves 
the  term  "  segregation "  more  free  to  designate  the  combined  action  of  the  prin- 
ciples producing  the  demarcation  of  groups  and  of  those  producing  the  intensifi- 
cation of  the  characters  of  the  separated  groups.  Partition  and  isolation  pro- 
duce habitudinal  and  racial  demarcation,  while  election  and  selection  produce 
habitudinal  and  racial  intensification,  and  the  combined  action  of  the  four 
principles  produces  segregation  both  racial  and  habitudinal.  (For  a  fuller  state- 
ment see  Chapters  V  and  VI.) 

♦As  this  explanation  does  not  occur  in  the  original  paper  it  is  printed  in 
different  .form. 


176  APPENDIX  I — DIVERGENT  EVOLUTION. 


4.  Classified  Table  of  Forms  of  Segregation* 
DEMARCATIONAL  SEGREGATION  [OR  ISOLATION]. 

A.  Environal  segregation: 

(a)   Industrial  segregation. 

Sustentational i 

Defensive 2 

Nidificational   3 

(6)  Chronal  segregation. 

Cyclical    4 

Seasonal 5 

(c)  Spatial  segregation. 

Geographical      (Migrational    6 

Local  I   •^Transportational 7 

)     vGeological    8 

(d)  Fertilizational  segregation   g 

(c)  Artificial  segregation. 

B.  Reflexive  segregation : 

(a)  Conjunctional  segregation: 

Social 10 

Sexual II 

Germinal 12 

Floral 13 

(b)  Impregnational  segregation: 

vSegregative  size    14 

Segregative  structure 15 

Potential  segregation ig 

Segregate  fecundity 17 

Segregate  vigor 18 

Segregate  adaptation 19 

Segregate  freedom  from  competition    20 

Segregate  escape  from  enemies   21 

(c)  Institutional  segregation. 

INTENSIVE  SEGREGATION. 

(a)  Assimilational  intension.  (e)  Amalgamational  intension. 

(6)  Stimulational  intension.  (/)  Selectional  intension. 

(c)  Suetudinal  intension.  (g)  Fecundal  intension. 

(d)  Emotional  intension.  (h)  Eliminational  intension. 

*  Numerals  are  attached  to  the  forms  of  segregation  found  in  natural  species. 


COMPUTATIONS  OF  EFFECTS. 


177 


5.  Computation  of  the  Effects  of  Different  Degrees  of  Positive  Segregation 
Cooperating  with  Different  Degrees  of  Segregate  Survival. 

Of  the  tables  which  are  herewith  presented  Table  I  is  an  arithmet- 
ical computation,  showing  the  number  of  half-breeds  as  contrasted 
with  the  pure-breeds,  when  nine-tenths  of  each  variety  form  unions 
among  themselves  and  double  with  each  generation,  while  the  off- 
spring of  the  one-tenth  that  form  mixed  unions  simply  equal  the 
number  of  the  parents  by  which  they  are  produced ;  in  other  words 
when  c  =  0.1,  M  =  2,  rn  =  i  (see  Table  II). 

Table  I. 


Variety  No.  1,  pure-breeds. 


1,000   =  A 

1.8 

1,800   =  A  (1.8) 

1.8 

3.240   =  A(i.8)« 

1.8 

5,832    =A(i.8)' 

357-05=  (i-S)*"  comput- 
ed by  log.  .•.357,050  = 
A(i.8)»«    

39.347272  =  (i.8)i« 

.■•39,347,272  =  A(i.8)i«. 


Of  what  gener- 
ation. 


Initial  number 
I  St  generation. 
2d  generation. 
3d  generation. 

10th  generation 
1 8th  generation 


Half  of  the 
half-breeds. 

Three- 
quarter 
breeds 
on  one 
side. 

100 
260 

532 

35, 688 
3,934.725 

20 

72 

Variety  No.  2, 
pure-breeds. 


I,  800 
3,  240 

5,832 

357,050 
39,347,272 


Explanation  of  Table  I. 

The  2d  generation  of  the  half-breeds  is  found  by  taking  nine-tenths  of  the  pre- 
vious half-breeds,  i.  e.,  100  X  0.9  =  90,  and  one-tenth  of  the  previous  pure-breeds 
(the  one-tenth  that  form  mixed  unions),  minus  one-tenth  of  the  previous  half- 
breeds  (because  one-tenth  of  the  half-breeds  consort  with  an  equal  number  of 
pure-breeds,  and  so  produce  not  half-breeds  but  three-quarter  breeds),  i.  e., 
1 80 —  10  =  170.  Adding  these  two  sums  together  we  have  90  -j-  170  =  260  = 
the  2d  generation  of  half-breeds. 

As  in  this  table  the  computation  commences  without  any  half-breeds,  the  fol- 
lowing generations  of  half-breeds  are  all  a  little  less  than  one-tenth  as  large  as  the 
corresponding  generations  of  pure-breeds.  When,  however,  we  come  to  the  i8th 
generation  the  difference  is  less  than  one  in  a  million,  and  we  may  consider  the 
result  as  practically  corresponding  with  the  formula  for  the  nth  generation  given 
in  Table  III. 


178 


APPENDIX   I — DIVERGENT   EVOLUTION. 


Table  II  is  a  preliminary  formula  for  showing  the  proportion  of 
half-breeds  to  pure-breeds. 

Let  /?  =  I  —  c  =  the  ratio  of  pure  breeding,  i.  e.,  the  segregation. 

Let  c  =  the  ratio  of  cross-breeding,  i.  e.,  the  segregation  viewed  from  the  other 
side. 

Ex. — When  nine-tenths  of  the  unions  are  within  the  Umits  of  the  species  and  one- 
tenth  of  the  unions  are  with  an  allied  species  R  —  0.9,  c  =  0.1.  R  will  always 
equal  i  —  c. 

Let  M  =  the  ratio  of  fertility  in  each  generation  for  those  that  breed  with  their 
own  kind. 

Let  m  =  the  ratio  of  fertility  in  each  generation  for  the  cross-unions  and  for 
the  hybrids  when  breeding  together. 

Let  A  =  the  initial  number  of  individuals  representing  the  pure  species  when 
the  computation  commences. 

TABI.E   II. 


Number  of  individuals  representing 
the  pure  form. 


Number  of  individuals  representing  the  half-breeds. 


_        A  =  Initial  number. 

A(RM)    =  1st  generation. 

A(RM)^  =  2d  generation. 

A(,RM)^  =  3d  generation. 

A(,RM)*  =  4th  generation. 

Substituting  (1  —  c)  for  J?  in  the  2d 

generation,  we  have  A  (Af  — 

Mcy  —  2d  generation. 


1st  generation  --  Acm. 

2d  generation  =  (AcmR  +  A(RM)c  —  Acme)  X  m. 
2d  generation  =  (AcmR  —  Acmc)m  +  Acm,{RM). 
2d  generation  —  Acm(,R  —  c)vt  +  Acm{RM). 

Substituting  in  this  (1  —  c)  for  R,  we  have 
2d  generation  =  Acm{\  —  2c)»t  -^  Acm{.M  —  Mc). 


Explanation  of  Table  II. 

The  term  AcmR  represents  the  number  of  half-breeds  that  form  unions  among 
themselves,  the  offspring  being  half-breeds;  A{RM)c  represents  the  total  number 
of  pure-breeds  of  the  ist  generation  that  form  mixed  unions;  of  these  Acme  form 
unions  with  an  equal  number  of  half-breeds,  and  their  offspring  being  three- 
quarter  breeds  must  be  rejected;  the  remainder,  namely,  A{RM)c  —  Acme,  form 
unions  with  the  other  race,  and  their  offspring  are  half-breeds  of  the  2d  generation. 


TABLE   III. 


179 


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•t,   5  & 


l8o  APPENDIX   I — DIVERGENT   EVOLUTION. 

Method  of  using  Table  III  (seep.  179). 

By  supposing  n  to  be  an  indefinitely  high  number,  and  by  giving 
different  values  to  M,  m,  and  c,  we  shall  have  the  means  of  contrast- 
ing the  number  of  the  pure-breeds  with  that  of  the  half-breeds,  when 
the  process  has  been  long  continued  under  different  degrees  of  posi- 
tive segregation  and  segregate  fecundity. 

In  the  first  place,  let  us  take  a  case  in  which  there  is  no  segregate 
fecundity,  that  is  M  =  m,  and  for  convenience  in  computation  let 
us  make  M  =  i,  m  —  i.  In  every  case  where  there  is  not  inte- 
grate fecundity,  that  is,  where  m  is  not  larger  than  M,  the  fraction 

M  M  ^^  ^^^^  than  unity,  and  the  sum  of  the  geometrical  pro- 
gression of  our  formula  will  fall  within  the  limits  of  a  number  that 
can  be  easily  computed  by  the  well-known  formula  5  =  ,  in  which 

a  is  the  first  number  of  the  progression,  which  in  this  case  is  i ,  and  r  is 
the  ratio  of  progression,  which  in  this  case  is  \f      ly^  the  fraction 

we  are  now  considering.     Supposing  c  =  — ,  the  fraction  will  be 

r      2 1 
1 1  —  —  I 

r~  =  0=''   ■'■    ^  =  r=-r  becomes   5  - g  -9-8 

I  —  —  ^  I 

10  9 

=  9.  This  number  9  is,  therefore,  equal  to  the  sum  of  this  progres- 
sion andean,  therefore,  be  used  as  the  value  of  the  infinite  progression 
in  the  formula  for  the  wth  generation  when  n  is  a  high  number. 
Substituting  these  values  in  the  last  formula  of  the  table,  we  find  that 
the  wth  generation  of  the  half-breeds  equals  the  wth  generation  of  the 

pure  forms,  each  being  equal  to  -^  of  ^  (M  —  Mc)''—K    A(M  —  Mc^—^ 

is  a  vanishing  quantity,  for  M  —  Mc  is  less  than  i .  Every  form  is, 
therefore,  in  time  fused  with  other  forms.     But  let  us  try  higher 

degrees  of  segregation.     If  we  make  c  = or  -,  we  still  find 

*  '^    '^  100        1000 

that  half-breeds  =  pure-breeds,  while  the  latter  are  constantly  de- 
creasing, which  shows  that  imperfect  positive  segregation,  without 
the  aid  of  some  degree  of  segregate  survival,  can  not  prevent  a  species 
being  finally  fused  with  other  species.  The  pure-breeds  must  de- 
crease as  long  as  the  whole  number  of  each  successive  generation  of 
pure-breeds  does  not  increase  by  a  multiple  equal  to  or  larger  than 

.     That  is,  if  m  =  M,  and  il  f  < fusion  will   in   time 

I  —  c  '  ^  I  —  c 

become  complete. 


Table  iv  with  formula.  i8i 

Let  us  now  consider  cases  in  which  the  segregation  is  incomplete, 
but  segregate  fecundity  comes  in  to  modify  the  result.     Let  M  ==  2, 

m  =z  I,  c  =  — .     Substituting  these  values  in  our  formula  from  Table 

.    9       18 
III,  we  shall  find  that  the  sum  of  the  infinite  progression  is  -  =  — . 

18 
And  M  —  Mc  =  — ,  which  makes  the  half-breeds  =  the  pure  forms  x 

cm;  and  cm  =      .     Let  M  =  2,  m  =  i,  c  = ;  then  half-breeds  = 

ID  '  '  100' 

pure  forms  x  .     Let  M  =  2,  m  =   i,  c  =     ;  then  the  infinite 

^  100  '  2 

progression  =  1,  M  —  Mc  =  i,  and  the  pure  forms  in  each  genera- 
tion will  equal  A ,  and  the  half-breeds  Ax.     Therefore,  half-breeds  = 

pure-breeds  x  -. 

Table  IV. — Simplified  Formulas  for  the  Proportions  in  which  Half-breeds  stand  to 
Pure-breeds  when  all  forms  of  Segregate  Survival  are  considered. 

In  each  formula  M  may  represent  the  ratio  of  those  coming  to 
maturity  in  each  generation  of  the  pure-breeds,  and  m  may  represent 
the  ratio  of  success  or  failure  of  the  cross-breeds  in  coming  to  maturity 
in  each  generation. 

From  Table  III  we  learn  that 

H  mc  r     ,    (i  —  2c)m       f  i  —  2c)m  1  ^  ,    T  1  ^       f  ^        1 

P~M-Mc^[    ^  M  —  Mc^  [M  —  Mc  j    "^IJ  |^J"*"J- 

When  (i  —  2c)m  is  less  than  M  —  Mc,  the  series  within  the  brack- 
ets is  a  decreasing  geometrical  progression,  and  we  may  obtain  the 

value  of  the  whole  series  by  the  formula  5  =  ^3— .     Applying  this 

formula  we  have 


P      M-Mc  "^         (i  —  2c)m 
^       M—Mc 

mc  M  —  Mc 


M  —  Mc     M  —  Mc  —  m+2mc 

=  M-m+7L-M)c ^°""^^^  (^) 

^==^^M-m+Zm-M)c ^°"""^^  ^^^ 


l82 


APPENDIX  I — DIVERGENT  EVOLUTION. 


The  following  solutions,  as  well  as  those  given  in  Table  V,  are 
obtained  by  substituting  values  for  M,  m,  and  c  in  formula  (2) : 
When  M  =  4,  w  =  3,  then  if 

c  =  i,  half-breeds  =  pure-breeds  x  f . 
c  =  ^,  half-breeds  =  pure-breeds  x  f- 
c  =  \,  half-breeds  =  pure-breeds  x  %. 
c  =  4-,  half-breeds  =  pure-breeds  x  f. 
c  =  ^,  half-breeds  =  pure-breeds  x  i  • 

Table  V. — From  Formula  (2). 


When  A/  =  10 

and  m  — 

9. 

8. 

7. 

6. 

5. 

4. 

3. 

2. 

1. 

If  c  -  y  then  half-breeds) 
=  pure-breeds  X      ) 

9 

8 

7 

6 

5 

4 

3 

2 

1 

10 

10 

10 

10 

10 

10 

10 

10 

10 

li  c  ^  -,  H  =  P  X 

9 

8 

7 

6 

5 

4 

3 

2 

1 

11 

12 

13 

14 

15 

16 

17 

18 

19 

If  c  -  i,  //  =  P  X 

9 

8 

7 

6 

5 

4 

3 

2 

1 

12 

14 

16 

18 

20 

22 

24 

26 

28 

If  c  =  i  //  =  P  X 

9 

8 

7 

6 

5- 

4 

3 

2 

1 

13 

16 

19 

22 

25 

28 

31 

34 

37 

If  c  =-.//  =  P  X 

9 

8 

7 

6 

5 

4 

3 

2 

1 

6 

14 

18 

22 

26 

30 

34 

38 

42 

46 

If  c=^,H  =  PX 

9 

8 

7 

6 

5 

4 

3 

2 

1 

7 

15 

20 

25 

30 

35 

40 

45 

50 

55 

If  c  =  i  W  =  P  X 

9 

8 

7 

6 

5 

4 

3 

2 

1 

9 

17 

24 

31 

38 

45 

52 

59 

66 

73 

If  c  =/•//=  P  X 

9 

8 

7 

6 

5 

4 

3 

2 

1 

10 

18 

26 

34 

42 

50 

58 

66 

74 

82 

If  c  =.-,//  =  P  X 

9 

8 

7 

6 

5 

4 

3 

2 

1 

100' 

108 

206 

304 

402 

500 

598 

696 

794 

892 

^f  c  -  ,^^.  H-  P  X 

9 

8 

7 

6 

5 

4 

3 

2 

1 

1000 

1008 

2006 

3004 

4002 

5000 

5998 

6996 

7994 

8992 

Observations  on  Table  V. 

This  mathematical  analysis  of  the  effects  of  positive  segregation 
and  segregate  fecundity  when  cooperating  brings  distinctly  into  view 
several  important  relations. 

First.  Incomplete  forms  of  positive  segregation,  that  avail  little 
or  nothing  in  preventing  a  form  from  being  absorbed  in  the  course  of 
time,  become  very  efficient  when  strengthened  by  moderate  degrees 
of  mutual  sterihty.     Take,  for  instance,  the  line  of  the  table  in  which 

c  =  — —     If  I  in  every  loo  unions  is  a  cross  with  some  other  form, 

I  GO 


OBSERVATIONS   ON   TABLE   V.  1 83 

the  form  will  in  time  be  overwhelmed,  unless  other  causes  come  in  to 
counteract ;  but  here  we  see  that,  if  segregate  fecundity  occurs  in  the 
ratio  of  10  to  9,  the  pure  form  becomes  12  times  as  numerous  as  the 
half-breeds;  and  if  in  the  ratio  of  10  to  5,  it  becomes  100  times  as 
numerous. 
Second.  Again,  if  we  take  the  proportional  differences  between  the 

different  terms  of  the  top  line  opposite  c  =  - ,  we  shall  find  them  very 

unlike  the  differences  that  appear  in  the  bottom  line  opposite  c  = . 

In  the  former  the  first  term  is  9  times  as  large  as  the  last,  while  in  the 
latter  the  first  term  is  more  than  80  times  as  large  as  the  last.  This 
shows  that  when  positive  segregation  is  intense,  differences  in  the 
degree  of  segregate  fecundity  produce  greater  contrasts  than  the 
same  differences  do  when  the  positive  segregation  is  slight. 

Third.  A  similar  distinction  is  found  when  we  compare  the  right- 
hand  column  with  the  left-hand  column.  The  smallest  term  in  the 
former  is  to  the  largest  term  in  the  same  column  as  i  to  899,  while  in 
the  left-hand  column  the  greatest  is  as  i  to  100.  This  shows  that 
when  segregate  fecundity  is  strongly  developed,  differences  in  the 
degrees  of  positive  segregation  produce  greater  contrasts  than  the 
same  differences  produce  when  the  segregate  fecundity  is  but  slightly 
developed. 


APPENDIX  II. 

INTENSIVE   SEGREGATION,    OR    DIVERGENCE   THROUGH 
INDEPENDENT  TRANSFORMATION.* 

I.  Classification  of  the  Forms  of  Intensive  Segregation. 

In  a  previous  paper  on  divergent  evolution  I  have  enumerated  many 
classes  of  natural  causes  which  produce  either  separate  or  segregate 
generation,  t  and  which,  in  their  combined  action,  tend  to  produce 
cumulative  segregation  and  divergent  evolution  in  every  part  of  the 
organic  world.  I  have  there  shown,  with  sufficient  fulness,  that  cumu- 
lative segregation  always  produces  cumulative  divergence  or  poly- 
typic evolution ;  but  I  have  not  fully  shown  how  separation  from  the 
first  involves  more  or  less  segregation,  or  how  segregation,  which  at 
first  divides  the  species  into  sections  with  reference  to  some  one  en- 
dowment, is  always  tending  toward  intensified  segregation  in  which 
the  sections  present  differences  in  regard  to  an  increasing  number  of 
endowments. 

After  expounding  the  principles  on  which  these  laws  of  divergence 
rest,  I  will  give  a  few  examples  of  divergence,  calling  attention  to  the 
complete  correspondence  between  the  facts  of  nature  and  the  prin- 
ciples expounded  in  this  and  the  previous  paper. 


*  From  the  Linnean  Society's  Journal,  Zoology,  vol.  xxrii.  Read  December 
19,  1889. 

t  Separate  generation,  or  separation,  is  the  indiscriminate  division  of  a  species 
into  sections  that  do  not  intergenerate.  Segregate  generation  or  segregation  is 
the  independent  generation  of  different  sections  of  a  species  when  the  sections  are 
composed  of  somewhat  divergent  classes  of  variations.  Isolation  differs  from 
selection  in  that  the  latter  denotes  the  exclusion  of  certain  kinds  from  opportunity 
to  propagate,  while  the  former  denotes  the  division  of  those  that  propagate  into 
classes  that  are  prevented  from  intergenerating.  Isolation,  or  the  prevention 
of  intergeneration,  whether  it  be  through  separation  or  segregation,  I  also  call 
independent  generation.  Darwin  used  isolation  as  equivalent  to  geographical 
separation,  while  later  writers  have  come  to  use  it  as  equivalent  to  independent 
generation. 

185 


l86  APPENDIX   II — INTENSIVE   SEGREGATION. 

1 .  Separation  always  Involves  more  or  less  Segregation,  for  no  two  Portions  of  a 
Species  Possess  exactly  the  Same  Azerage  Character. 

When  a  homogenous  species  is  divided  into  two  large  sections,  it 
may  be  difficult  to  prove  by  measurement  that  there  is  any  difference 
in  their  average  character ;  but  on  general  principles  we  may  assume 
that,  at  least  in  some  points,  there  is  a  slight  difference.  It  is  evident 
that  when  the  separated  sections  are  small  there  is  more  likely  to  be 
diversity  in  the  average  character  of  the  sections  and  that,  roughly 
stated,  the  probability  of  divergence  from  this  cause  will  be  in  direct 
proportion  to  the  variableness  of  the  species  and  in  inverse  proportion 
to  the  size  of  the  different  sections.  When  a  few  stragglers  form  a 
small  colony  in  an  isolated  position  there  is  the  strongest  reason  to 
expect  that  they  will  not  be  able  to  propagate  the  characters  of  the 
species  in  exactly  the  same  proportions  in  which  they  are  produced  by 
the  main  body  of  the  species,  or  by  any  other  small  colony  that  is  prop- 
agating independently ;  and  when  the  original  stock  has  been  rendered 
highly  variable  by  the  crossing  of  somewhat  divergent  varieties,  the 
degree  of  difference  that  will  probably  be  presented  by  any  two  inde- 
pendent colonies  will  be  correspondingly  increased.  We  must  bear  in 
mind  that  while  specimens  possessing  an  average  character  in  any  one 
respect  are  always  abundant,  those  perfectly  representing  the  average  in 
every  respect  are  rarely,  if  ever,  found.  Now,  is  it  to  be  supposed  that 
any  one  or  any  small  number  of  these  imperfect  representatives  of  a 
species  will,  if  separated  from  the  rest,  transmit  all  the  characteristics 
of  that  species  in  the  exact  proportions  presented  by  the  average  char- 
acter of  the  original  stock  ? 

Mr.  Francis  Galton  has  conclusively  shown*  that  in  the  children  of 
parents  whose  heights  deviate  from  the  average  of  the  race  to  which 
they  belong,  there  will  be  a  similar  deviation  amounting  on  the  average 
to  a  certain  fixed  proportion  of  that  presented  by  what  he  calls  the 
mid-parentage.  The  mid-filial  deviation  in  the  groups  investigated 
by  him  was  about  two-thirds  of  the  mid-parental  deviation.  There 
is,  therefore,  a  regression  in  the  average  character  of  the  offspring 
toward  the  typical  character  of  the  group.  It  must  be  observed,  how- 
ever, that  this  law  can  hold  in  full  force  only  when  there  has  been  free 
crossing,  for  otherwise  there  will  be  no  type  from  which  the  deviation 
can  be  measured. 


*  See  "Types  and  Their  Inheritance,"  an  address  before  the  Section  of  Anthro- 
pology of  the  British  Association  in  1885;  also  "Natural  Inheritance,"  p.  97. 


TRANSFORMATION  AND  MONOTYPIC  EVOLUTION.        1 87 

2.  Eight  Forms  of  Monotypic  Evolution. 

Let  us  now  consider  how  this  initial  segregation,  which  is  always 
present  in  the  case  of  a  small  colony,  is  enhanced  and  intensified  by  the 
cooperation  of  other  principles,  and  how  forms  segregated  through 
possessing  different  characters  in  some  one  respect  come  to  diverge  in 
other  respects.  For  example,  when  differences  of  color  become  the 
occasion  for  sexual  and  social  segregation,  how  does  this  open  the  way 
for  divergent  transformation  in  habits  of  feeding  and  in  a  thousand 
other  respects  ?  The  principles  cooperating  with  independent  genera- 
tion in  producing  this  enhanced  divergence  are  all  causes  of  simple 
transformation,  or  monotypic  evolution  when  there  is  free  intergen- 
eration.  Divergent  breeds  of  domestic  animals  have  always  been 
produced  when  the  different  sections  of  a  species  in  the  care  of  different 
races  of  men  have  been  prevented  from  interbreeding,  thus  securing 
their  independent  transformation  during  the  process  of  domestication. 
So  in  nature,  when  any  form  of  independent  generation  has  been 
established,  any  cause  of  transformation  that  may  afterwards  arise 
will  always  produce  more  or  less  divergent  evolution,  and  never  that 
which  is  in  every  respect  parallel.  But  we  must  defer  the  discussion 
of  this  subject  till  we  have  enumerated  the  more  manifest  of  the  prin- 
ciples of  monotypic  evolution : 

(i)  Assimilational  transformation,  or  modification  due  to  deficiency 
with  economy,  or  redundance  with  profusion,  of  growth,  resulting 
from  different  degrees  of  assimilative  power.  ' '  Economy  of  growth  " 
is  a  term  already  in  use,  but  a  term  is  needed  that  shall  include  both 
this  and  its  opposite. 

(2)  Stimulational  transformation,  or  modification  produced  by 
changed  motions  in  the  fluids  of  the  organism  responsive  to  changed 
influences  in  the  environment.  Under  this  principle  we  may  place 
the  direct  influences  of  light,  heat,  electricity,  the  dampness  of  the  air 
or  the  saltness  of  the  water  in  which  the  organism  is  bathed,  the  qual- 
ity of  the  food,  and  all  stimulation  from  physical  and  chemical  causes, 
exclusive  of  those  resulting  in  muscular  activity  or  the  movement  of 
the  organs. 

(3)  Suetudinal  transformation,  or  modification  due  to  the  effects  of 
use,  disuse,  and  habitual  effort  in  producing  motions,  and  in  resisting 
the  strain  of  gravity  and  other  forces  tending  to  produce  motion.  Sue- 
tude  is  not  found  in  the  dictionary,  but  I  venture  to  use  it  as  including 
assueiiide,  which  is  being  accustomed  to,  being  practiced  in,  habitual 
use ;  and  desttetude,  which  is  disuse,  discontinuance  of  practice. 


1 88  APPENDIX   II — INTENSIVE   SEGREGATION. 

(4)  Emotional  transformation. — Dr.  C.  V.  Riley,  late  of  the  National 
Museum,  Washington,  has  called  attention  to  the  influence  of  parental 
emotions  (especially  maternal  emotions  during  the  term  of  pregnancy) 
as  a  factor  in  evolution  (Address  "On  the  Causes  of  Variation,"  before 
the  Section  of  Biology,  American  Association,  August,  1888;  also  in 
Popular  Science  Monthly,  vol.  xxxlv,  pp.  811-816). 

(5)  The  cumulative  development  of  adaptations  through  "the 
survival  of  the  fittest"  when  the  fittest  are  other  than  average  forms. 
This  is  the  principle  of  unbalanced  selection  producing  selectional 
transformation. 

(6)  Transformation  produced  by  the  indiscriminate  destruction  of 
a  portion  of  a  species,  with  the  accompanying  probability  that  the 
remaining  portion  will  not  possess  all  the  characters  possessed  by  the 
species  previous  to  the  elimination.  This  principle  I  call  "unbalanced 
indiscriminate  elimination,"  producing  indiscriminate  eliminational 
transformation. 

(7)  Transformation  produced  by  different  degrees  of  amalgama- 
tion of  the  varieties  and  races  which  have  resulted  from  previous  segre- 
gations. In  most  species  there  is  a  constant  process  of  amalgamation 
by  which  thousands  of  minor  varieties  are  absorbed;  but  when  the 
process  extends  beyond  ordinary  limits,  and  the  barriers  that  have 
divided  well-marked  races  give  way,  transformation  must  follow. 
This  principle  I  call  diversity  of  amalgamation  producing  amalgama- 
tional  transformation. 

(8)  The  cumulative  development  of  the  more  fertile  of  the  forms 
that  are  equally  adapted.  In  other  words,  transformation  produced 
by  diversity  in  the  relative  fertility  of  varieties  that  are  equally 
adapted  to  the  environment  and  the  constitution  of  the  species,  or  by 
change  in  the  degrees  of  fertility  possessed  by  the  same  variety  at  dif- 
ferent times  and  in  different  places.  This  principle  I  call  unbalanced 
fecundity,  or  unbalanced  fecundal  selection,  producing  fecundal  trans- 
formation. 

Of  these  principles  all  except  the  sixth,  seventh,  and  eighth  have 
been  more  or  less  discussed  by  writers  on  biology,  though  some  of  the 
forms  of  selection  depending  on  the  relations  in  which  the  members 
of  a  species  stand  to  each  other  have  never  been  pointed  out,  and 
many  writers  have  failed  to  observe  that  selection  often  produces  fixity 
of  type  instead  of  transformation,  and  that  divergence  can  not  be  pro- 
duced through  diversity  in  the  kinds  of  selection  without  the  coopera- 
tion of  isolation,  and  may  be  produced  without  exposure  to  different 
environments. 


LAWS  OF  GROWTH  NOT  DISCUSSED.  1 89 

Assimilational,  stimulational,  suetudinal,  and  emotional  transfor- 
mation belong  to  a  class  of  factors  producing  what  are  known  as  ac- 
quired characters.* 

Selectional,  eliminational,  amalgamational,  and  fecundal  transfor- 
mation may  be  classed  as  principles  of  unbalanced  propagation.  The 
principles  of  unbalanced  propagation  are  abundantly  established  as 
genuine  methods  of  change  in  the  average  inheritable  characters  of 
species,  not  only  by  experience  derived  from  the  domestication  of 
plants  and  animals,  but  by  observation  of  similar  effects  produced  by 
natural  processes. 

3.  Principles  of  Vital  Action  not  here  Discussed. 

I  have  not  mentioned  "acceleration  and  retardation"  as  principles 
of  transformation,  for  they  seem  to  be  but  phases  of  the  law  of  sue- 
tude ;  for,  as  explained  by  Cope,  use  or  effort  in  the  parents  produces 
in  the  offspring  accelerated  inheritance,  while  disuse  or  cessation  from 
effort  produces  in  the  offspring  retarded  inheritance,  f  So  also 
Hyatt's  "Law  of  Concentration"  (or  "acceleration,"  as  he  often  calls 
it)  seems  to  be  a  general  law  of  inheritance  relating  to  the  transmis- 
sion of  characters  originating  under  any  and  every  principle,  the 
effects,  whether  progressive  or  retrogressive,  being  inherited  at  earlier 
and  earlier  ages  in  each  successive  generation.  J  It  is  also  doubtful 
whether  correlated  transformation  should  be  considered  a  separate 
principle,  for  it  seems  to  be  simply  the  inheritance  by  offspring  of 
characters  that  have  for  generations  been  united  in  the  endowments 


*  These  four  factors  are  included  under  what  Prof.  J.  M.  Baldwin  calls  accom- 
modation (see  Nature,  April  15,  1897,  also  "Development  and  Evolution," 
pp.  94  and  151).  Accotnnwdation  produces  three  classes  of  effects:  (i)  Habitual 
activity  {that  is,  repeated  imitative  and  intelligent  activities,  aiding  in  self-preserva- 
tion, or  in  the  preservation  of  offspring  or  of  the  communal  group);  (2)  modification 
{that  is,  acquired  physiological  and  anatomical  effects  of  activity);  (3)  active  {or 
endonomic)  selection  determtfted  by  the  habitual  activities  of  the  group  in  dealing  with 
the  environment.  For  a  description  of  accommodation  in  lower  organisms  see 
Contributions  to  the  Study  of  the  Behavior  of  Lower  Organisms,  published  by 
the  Carnegie  Institution,  1904,  where  Herbert  S.  Jennings  has  shown  in  a  series 
of  elaborate  experiments  with  Amoeba,  with  ciliate  infusoria,  and  with  flagel- 
lates, that  their  usual  method  of  response  to  any  given  stimulus  is  in  accord 
with  what  Lloyd  Morgan  has  called  "The  method  of  trial  and  error."  This 
method  I  would  describe  as  varied  tentative  action  with  repeated  response  till 
success  is  gained  either  by  avoiding  damage  or  by  attainmg  advantage. 

t  "Origin  of  the  Fittest,"  pp.  203-207,  228. 

X  Proceedings  of  the  American  Association,  vol.  xxxii,  pp  352-361. 


I90  APPENDIX   II — INTENSIVE   SEGREGATION. 

of  at  least  a  portion  of  their  ancestry,  and  the  correlation  of  these 
endowments  must  have  been  produced  through  the  action  of  other 
principles. 

The  prevalence  of  males  in  times  of  pressure,  with  the  prevalence  of 
females  in  times  of  plenty,  is  regarded  by  Dr.  W.  K.  Brooks,  of  Johns 
Hopkins  University,  as  a  characteristic  established  by  natural  selec- 
tion, by  which  the  organism  acquires  variability  or  fixity  of  type 
according  as  either  character  is  most  needed;  for  according  to  his 
observations  the  males  represent  the  former  and  the  females  the  latter 
element.  There  can  be  no  doubt  that  in  many  species  the  males  are 
more  variable  than  the  females,  and  that  in  some  of  the  same  species 
the  proportion  of  males  increases  with  the  degree  of  adversity;  but 
this  does  not  seem  to  be  sufficient  ground  for  maintaining  that  the 
increase  in  the  proportion  of  males  will  increase  the  variability  of 
the  offspring.  Increase  in  the  number  or  amount  of  the  variable 
element  does  not  necessarily  involve  increase  in  the  variability  of 
either  element  or  in  the  offspring  of  both.  I  find  need  of  additional 
factors  in  order  to  bring  these  facts  into  any  relation  to  the  increase 
of  variability.  Granting  that  the  sperm-cell  is  the  source  of  variation 
and  the  germ-cell  the  source  of  fixity,  and  that  increased  tendency 
to  variation  in  the  offspring  will  be  secured  by  an  increased  range 
of  variation  in  the  sperm-cells,  it  does  not  follow  that  increase  in 
the  relative  number  of  males  will  increase  the  rahge  of  variation  in 
the  sperm-cells,  and,  therefore,  in  the  offspring.  But  if  conflict  in  the 
environment  and  the  winnowing  process  of  natural  selection  falls 
most  heavily  upon  the  males,  there  must  be  some  advantage  in  having 
their  relative  numbers  increased  in  times  of  adversity;  and  if  the 
exposure  of  parents  to  hardships  increases  the  variability  of  either 
male  or  female  offspring,  and  especially  if  it  increases  the  variability 
of  both,  plasticity  will  be  increased. 

Professor  Cope's  "Doctrine  of  the  UnspeciaHzed "  (Origin  of  the 
Fittest,  pp.  232-235)  rests  on  the  fact  that  the  most  highly  specialized 
types,  as  well  as  individuals,  are  most  likely  to  be  exterminated  by 
extraordinary  changes  in  the  environment;  and  Mr.  Hyatt's  "Tera- 
tology" (Proceedings  American  Association,  vol.  xxxii,  pp.  349-360) 
teaches  that  types  that  are  being  slowly  exterminated  usually  assume 
forms  resembling  those  produced  by  old  age  and  disease  in  the  indi- 
vidual. These  and  other  laws  in  the  growth  and  decay  of  types 
and  individuals  are  of  great  interest,  as  they  afford  organic  condi- 
tions under  which  the  factors  of  transformation  must  act. 


INDEPENDENT  TRANSFORMATION   DIVERGENT.  I9I 

4.  The  Transformation  0}  Freely  Inter  generating  Organisms  Never 
Permanently  Divergent, 

I  mention  these  eight  principles  of  transformation,  not  with  the 
purpose  of  entering  upon  a  full  discussion  of  the  same,  but  simply  to 
point  out  the  relation  in  which  they  all  stand  to  divergent,  or  poly- 
typic, evolution.  It  is  evident  that,  whether  acting  separately  or 
together,  they  can  never  be  the  cause  of  divergent  evolution  in  organ- 
isms that  are  freely  intergenerating;  for  in  such  a  group  of  organisms 
whatever  modifies  one  part  of  the  group  in  characters  that  are 
inheritable  will,  ere  many  generations,  modify  the  whole.  If  the 
group  is  exposed  to  a  variety  of  inharmonious  conditions,  which,  with 
independent  generation  would  produce  divergent  character,  with  free 
intergeneration,  the  only  result  will  be  variation.  Without  indepen- 
dent generation  (or  isolation)  there  can  be  no  permanent  divergence. 

5.  Independent  Transformation  Always  Divergent. 

If  any  species  is  divided  into  two  or  more  sections  that  do  not  inter- 
generate  and  that  are  severally  subject  to  highly  complex  transform- 
ing influences,  it  may  only  be  by  a  series  of  coincidences  which  the 
reason  refuses  to  receive  as  in  the  slightest  degree  probable  that  any 
two  sections  will  be  modified  in  exactly  the  same  way.  This  high 
degree  of  probability,  amounting  to  a  certainty,  that  when  causes  of 
transformation  cooperate  with  causes  producing  isolation  the  result 
in  successive  generations  will  be  increasing  degrees  of  segregation  and 
of  divergence,  is  what  I  call  the  law  of  intensive  segregation.  The 
different  forms  of  this  principle,  resting  on  the  certainty  that  the 
cooperation  of  any  one  of  the  principles  of  transformation  with  any 
one  of  the  principles  of  independent  generation  will  produce  increas- 
ing segregation  with  increasing  divergence,  are  the  following : 

( 1 )  Assimilational  intension,  or  segregation  and  divergence  through  , 
independent  assimilation. 

(2)  Stimulational  intension,  or  segregation  and  divergence  through 
independent  stimulation. 

(3)  Suetudinal  intension,  or  segregation  and  divergence  through 
independent  suetude. 

(4)  Emotional  intension,  or  segregation  and  divergence  through 
independent  emotional  transformation. 

(5)  Selectional  intension,  or  segregation  and  divergence  through 
independent  selection. 

(6)  Eliminational  intension,  or  segregation  and  divergence 
through  independent  and  indiscriminate  elimination. 


192  APPENDIX   II — INTENSIVE   SEGREGATION. 

(7)  Amalgamational  intension,  or  segregation  and  divergence 
through  independent  amalgamation. 

(8)  Fecundal  intension,  or  segregation  and  divergence  through 
independent  fecundal  transformation. 

In  groups  that  do  not  intergenerate,  divergent  forces  reveal  them- 
selves whenever  transformation  is  introduced.  If  it  were  possible  to 
believe  that  the  effects  of  independent  selection  or  of  independent 
suetude  had  been  completely  parallel,  it  would  still  be  impossible  to 
believe  that  both  of  these,  together  with  the  remaining  six  principles 
of  transformation,  would  ever  so  combine  as  to  produce  completely 
parallel  transformation  in  isolated  sections  of  a  species,  even  if  all 
were  surrounded  by  the  same  environment.  This  principle  is  not 
inconsistent  with  the  introduction  of  what  Professor  Hyatt  calls 
"representative  of  parallel  characteristics"  in  two  or  more  divergent 
series  of  forms.  What  he  points  out  is  that,  under  the  influence  of 
heredity,  similar  organisms  exposed  to  similar  environments  undergo 
similar  transformation  (Anniversary  Memoirs  of  the  Boston  Society 
of  Natural  History,  1880:  "The  Genesis]  of  the  Tertiary  Species  of 
Planorbis  at  Steinheim,"  pp.  24-29). 

In  the  description  of  these  principles  I  have  used  the  adjective 
"independent"  to  signify  that  the  principle  is  operating  in  sections 
of  the  species  that  are  prevented  from  intergenerating.  In  the  term 
"independent  variation"  Mr.  Romanes  has  already  used  the  adjec- 
tive "independent "  as  meaning  "w/^ert  accompanied  with  the  prevention 
of  intercrossing." 

6.   The  Pervasive  Influence  of  the  Catises  of  Transformation  and  the 
Law  of  Intension. 

In  my  paper  on  "  Divergent  Evolution  "  I  made  the  statement  that 
' '  When  separate  generation  is  long  continued  we  have  reason  to  believe 
it  always  passes  into  segregate  generation  with  divergent  evolution." 
The  same  thought  had  been  expressed  in  a  previous  paper  by  the 
statement  that  "Variation  is  so  strong  that  all  that  is  necessary  to 
secure  divergence  of  types  is  to  prevent  their  intermingling."*  The 
certainty  that  independent  generation  with  transformation  will  never 
produce  parallel,  but  always  more  or  less  divergent  evolution  is  the  law 
of  intensive  segregation  already  referred  to.  But  in  addition  to  this  cer- 
tainty there  is  a  very  strong  probability  that  where  independent  gen- 
eration is  long  continued,  transformation  of  some  kind  will  supervene. 
If  there  are  any  species  in  which  the  power  of  cumulative  variation  has 


*  See  "  Diversity  of  Evolution  under  One  Set  of  External  Conditions."   Joum. 
I^inn.  Soc,  Zool.,  vol.  xi,  p.  499. 


THE   LAW   OF    INTENSION.  I93 

been  entirely  lost,  this  latter  law  can  not  hold  in  their  case ;  but  it  is 
doubtful  whether  among  species  that  reproduce  sexually  there  are 
many  such.  The  variability  of  some  species  is  so  small,  and  the  con- 
ditions of  the  environment  are  so  constant,  that  comparatively  long 
periods  of  independent  generation  pass  before  perceptible  transfor- 
mation arises.  This  seems  to  be  the  case  with  the  thirteen  and 
seventeen  year  races  of  Cicada  septendecim,  to  which  I  shall  refer  when 
giving  examples  from  nature.  From  the  high  probability  that  long- 
continued  independent  generation  (i.  e.,  isolation)  will  be  followed 
by  independent  transformation,  and  the  certainty  that  independent 
transformation  will  be  divergent,  there  follows  the  corollary  that 
long-continued  independent  generation  will  probably  be  attended  by 
divergence.  In  other  words,  independent  generation  long  continued 
is  almost  always  attended  by  independent  transformation ;  and  inde- 
pendent transformation  inevitably  produces  divergence.  This  double 
principle  I  call  the  law  of  intension.  This  law  rests  on  the  ubiquity 
of  transforming  influence  and  on  the  impossibility  that  in  a  species 
possessing  any  plasticity  the  inherited  effects  in  any  section  indepen- 
dently generating  should  be  exactly  the  same  as  in  any  other  section. 
This  is  especially  the  case  when  the  species  is  highly  plastic  and  when 
the  isolated  section  is  very  small. 

We  can  not  doubt  that  when  a  diversity  of  powers  and  suscepti- 
bilities in  the  different  sections  is  acted  upon  by  a  great  variety  of 
influences  the  responses  of  the  different  sections  will  be  unlike,  and 
the  result  will  be  increasing  segregation  and  increasing  divergence. 
Now,  it  is  impossible  to  doubt  that  in  species  propagating  sexually 
and  possessing  some  degree  of  plasticity,  these  are  exactly  the  con- 
ditions whenever  the  species  is  divided  into  sections  that  do  not  inter- 
generate. 

It  should  be  observed  that,  in  accordance  with  the  principle  of 
intension,  not  only  is  indiscriminate  separate  generation  when  long- 
continued  transformed  into  more  and  more  strongly  segregate  gen- 
eration, but  any  form  of  segregate  generation,  resting  on  some  one 
principle  that  causes  the  division  of  the  species  into  sections  differing 
in  regard  to  some  one  form  of  endowment,  will,  if  it  is  long  continued, 
be  inevitably  reinforced  and  intensified  by  transformations,  which, 
being  independently  combined  and  transmitted,  will  multiply  the 
number  of  characteristics  in  regard  to  which  divergence  takes  place. 
If,  for  example,  the  pollen  of  a  given  variety,  when  falling  upon  the 
stigma  of  the  same  variety  or  race,  is  prepotent  over  the  pollen  of 
every  other  variety  or  race  that  falls  Upon  the  same  stigma  at  the 


194  APPENDIX   II — iNT^NSlVe    SEGREGATION. 

same  time,  or  at  a  somewhat  earlier  time,  what  I  call  prepotential 
segregation  will  divide  the  species  into  two  groups  that  are  prevented 
for  the  most  part  from  intergenerating ;  and  these  separate  groups, 
gradually  coming  under  the  influence  of  different  degrees,  forms,  and 
combinations  of  the  transforming  principles,  will  in  time  become 
strongly  characterized  species.  It  is  not,  however,  necessary  that  all 
or  any  of  these  forms  of  transformation  should  cooperate  with  segre- 
gation in  order  to  produce  a  distinct  species.  The  accumulated 
effects  of  segregation,  unaided  by  these  principles  producing  intensi- 
fication, would  be  sufficient  to  produce  well-defined  species ;  but  it  is 
impossible  that  they  should  often  remain  unaided. 

7.   Utilitarian  and  Non-Utilitarian  Divergence. 

The  principles  of  suetude  and  selection,  though  they  are  directly 
related  to  the  development  of  utilitarian  characters,  may  produce  in 
the  useful  innate  characters  of  isolated  sections  of  the  same  species 
exposed  to  the  same  environment,  divergence  that  is  not  necessary 
or  advantageous ;  and  the  effects  of  the  other  six  principles  are  often 
not  only  wanting  in  but  opposed  to  utility.  Assimilational  transfor- 
mation includes  redundance  of  growth,  which  is  not  always,  as  well 
as  economy  of  growth,  which  is  always,  utilitarian.  Unbalanced 
elimination,  amalgamation,  and  fecundity  may  be  advantageous, 
useless,  or  disadvantageous.  We  have,  therefore,  in  these  six  prin- 
ciples of  transformation,  abundant  cause  for  the  introduction  of 
non-utilitarian  characters;  and,  when  accompanied  by  independent 
generation,  they  must  be  the  source  of  multitudes  of  non-utilitarian 
divergences.  In  the  earlier  stages  of  divergent  evolution  the  non- 
utilitarian  distinctions  are  more  abundant;  for  in  the  later  stages 
multitudes  of  them  are  weeded  out  by  economy  of  growth,  as  has  been 
clearly  pointed  out  by  Mr.  Romanes  ;*  and  still  others  through  com- 
ing under  new  conditions  in  the  environment  or  through  some  new 
habit  of  intelligence,  become  useful  endowments,  and  are  brought 
under  the  preserving  and  accumulating  influence  of  natural  selection 
or  of  suetude.  It  should,  however,  be  noted  that  the  development  of 
useful  specific  differences  is  as  much  due  to  independent  generation 
as  is  the  development  of  useless  specific  differences.  Diversity  of 
suetude  or  of  selection  does  not  produce  divergent  evolution  unless  it 
cooperates  with  independent  generation. 


*  Physiological  selection,  Joum.  Linn.  Soc,  Zool.,  vol.  xix,  p.  383. 


SEI^ECTIONAI,  INTENSION.  1 95 

8.  Selectional  Intension,  or  Segregation  and  Divergence  Produced  by 
Independent  Selection. 

That  we  may  gain  a  clear  apprehension  of  the  nature  and  influence 
of  this  principle,  certain  discriminations,  which  have  not  always  been 
recognized  by  writers  on  the  subject,  are  absolutely  necessary;  and, 
for  the  sake  of  avoiding  misunderstandings,  it  is  desirable  that  these 
distinctions  should  be  represented  by  clearly  defined  terms.  I  am 
fully  aware  that  many  will  be  opposed  to  the  introduction  of  new 
terms  into  the  treatment  of  a  subject  that  has  been  so  long  and  ably 
discussed.  If  these  discriminations  were  not  found  necessary  by  the 
author  of  the  "Origin  of  Species,"  or  if  the  distinctions,  so  far  as 
recognized  by  himself  and  others,  have  been  expressed  in  the  language 
of  ordinary  description,  why  should  a  more  accurate  terminology  be 
needed  now?  In  reply  it  may  be  said  that  the  freedom  from  tech- 
nical language,  which  is  a  great  advantage  in  a  work  which  for  the  first 
time  calls  the  attention  of  the  world  to  a  vast  subject,  is  a  serious 
defect  when  the  exact  relations  of  the  subject  come  under  discussion. 

In  order  to  secure  clear  thinking  on  the  subject,  I  have  found  it 
necessary  to  keep  the  following  distinctions  constantly  in  mind : 

(i)  The  selection  that  results  in  the  transformation  of  species  is  not 
the  selection  of  one  species  to  the  exclusion  of  another.  The  breeding 
of  the  horse  to  the  exclusion  of  the  ass  modifies  neither  the  one  nor  the 
other.  It  is  the  exclusive  generation  of  certain  variations  of  a  single 
intergenerating  group  that  gradually  transforms  the  group.  When, 
therefore,  we  speak  of  selection  as  a  cause  of  transformation,  we  refer 
to  the  selection  of  the  variations  that  are  to  interbreed  and  keep  up  the 
race,  to  the  exclusion  of  other  variations.  In  order  to  maintain  the 
same  distinction  in  the  nomenclature  of  natural  processes,  what  I  call 
*' selection"  is  caused  by  the  failure  of  certain  forms  of  a  species  to 
perpetuate  their  kind  as  contrasted  with  the  success  of  other  forms. 
If  the  failure  includes  all  the  forms  of  a  species,  I  call  it  the  extinction 
of  that  species  and  class  it  as  a  cause  of  transformation  in  the  remain- 
ing species  only  so  far  as  it  makes  a  change  in  their  environment. 

(2)  The  exclusive  generation  of  certain  forms  of  an  intergenerating 
group  does  not  necessarily  result  in  transformation.  Experiments  in 
artificial  breeding  show  that  if  we  select  only  the  typical  representa- 
tives of  a  race  the  general  character  of  the  race  is  not  changed,  though 
any  tendency  to  fluctuating  variation  may  be  gradually  diminished 
and  the  stability  of  the  type  increased.  When,  however,  one  form  of 
deviation  from  the  mean  is  constantly  selected  without  a  counterbal- 
ancing selection  of  the  opposite  deviation,  the  transformation  of  the 


196  APPENDIX  II — INTENSIVE   SEGREGATION. 

race  is  usually  the  result.  In  other  words,  balanced  selection  produces 
stability  of  type,  and  unbalanced  selection  produces  transformation  of  type.  * 

In  the  light  of  this  twofold  law  we  see  how  there  may  be  stringent 
selection  without  transforming  effect.  In  nearly  every  species  there  is 
a  constant  struggle  between  the  different  forms  of  variation ;  and  as  it 
never  happens  that  all  the  forms  are  equally  successful,  the  process  of 
natural  selection  is  always  bearing  in  full  force  upon  this  species.  If, 
then,  it  could  be  shown  that  natural  selection,  wherever  it  exists,  must 
necessarily  produce  transformation,  it  would  be  impossible  to  resist 
the  conclusion  that  nearly  every  species  is  undergoing  transformation 
through  this  cause.  But  it  is  unbalanced  rather  than  balanced  selec- 
tion that  produces  transformation.  We  also  see  that  heredity  tends 
to  make  the  most  successful  form  the  average  form,  and  thus  to  con- 
vert unbalanced  into  balanced  selection.  From  this  it  follows  that  in 
order  that  selection  should  produce  continuous  transformation,  cov- 
ering a  wide  range,  it  is  necessary  that  the  form  of  variation  selected 
should  from  time  to  time  be  changed.  This  may  be  expressed  as  the 
principle  of  continuous  transfonnation  through  successive  changes  in  the 
character  of  the  selection. 

Though  selection  produces  transformation  only  when  it  involves 
the  survival  of  other  than  typical  forms,  it  is  still  very  possible  that 
there  are  only  a  few  species  in  which  completely  balanced  selection 
prevails  for  very  many  generations  in  succession.  It  is  still  certain 
that  long-continued  independent  selection  gradually  passes  into  diver- 
sity of  selection  producing  divergent  evolution. 

(3)  Though  in  more  than  one  passage  Darwin  maintains  that  uni- 
formity of  external  conditions  involves  uniformity  of  natural  selec- 
tion, and  that  isolation  can  have  no  effect  in  transforming  a  species  if 
physical  conditions  and  surrounding  organisms  remain  the  same, 
still  I  think  that  if  the  question  had  been  distinctly  brought  before 
him  he  would  have  admitted  that  exposure  to  a  new  or  changed 
environment  was  not  a  necessary  condition  for  change  in  the  char- 
acter of  sexual  selection.  Now,  I  think  it  can  be  shown  that,  besides 
sexual  selection,  there  are  several  forms  of  selection  that  depend  upon 
the  relations  of  the  members  of  one  species  to  each  other  and  that 
may  undergo  change  without  the  organism  being  exposed  to  a  different 
environment. 

Selection  depending  on  the  relations  of  the  organism  to  the  envi- 
ronment I  call  environal  selection,  of  which  I  find  two  kinds,  namely, 


*  The  general  law  is  here  stated,  without  any  attempt  to  explain  why  selection, 
securing  the  exclusion  of  those  falling  below  a  certain  standard,  is  necessary  for 
the  preservation  of  that  standard  in  the  case  of  many  characters  (see  par.  (6)  below) . 


DIVERSITY  OF  SELECTION  THROUGH  DIVERSITY  OF'  USE.  I97 

active  and  passive  selection,  and  under  passive  selection  I  place 
natural  and  artificial  selection.  Selection  depending  on  the  relations 
of  the  members  of  a  species  to  each  other  I  call  reflexive  selection,  the 
chief  forms  of  which  I  call  conjunctional,  dominational,  impregna- 
tional,  and  institutional  selection.* 

(4)  It  must  be  carefully  noted  that  diversity  of  selection  depending 
on  diversity  in  the  relations  of  the  organism  to  the  environment  does 
not  necessarily  involve  the  exposure  of  the  organism  to  different 
environments.  In  other  words,  change  in  even  environal  selection 
does  not  necessarily  involve  either  change  in  the  environment  or  the 
entrance  of  the  species  into  a  new  district.  Darwin's  teaching  seems, 
at  times,  to  be  in  conflict  with  this  statement,  but  there  are  passages 
in  his  writings  which  distinctly  state  that  variations  in  instinct  may 
lead  to  different  habits  of  sustentation,  and  it  is  evident  that  this 
would  naturally  lead  to  a  difference  in  the  congenital  qualities  that 
win  success  in  the  different  sections  and  so  to  difference  in  the  envi- 
ronal selection. 

It  should  be  remembered,  however,  that  the  meaning  of  anyone's 
statements  on  this  subject  will  depend  on  his  definitions  of  the  words 
used.  What  is  meant  by  environment,  external  conditions,  and 
other  similar  terms  ?  Until  we  define  we  shall  only  beat  the  air,  how- 
ever exact  our  statements  may  seem  to  be.  I  therefore  repeat  what 
I  have  elsewhere  stated,  that,  according  to  my  definition,  change  in 
the  environment  is  always  change  in  activities  that  lie  outside  of  the 
species,  or  of  the  segregated  group,  of  individuals  that  is  under 
consideration.  In  Darwin's  usage  the  phrase  "change  in  external 
conditions  "  seems  to  carry  the  same  meaning ;  but  in  some  cases  this 
can  hardly  be  the  case. 

Diversity  in  the  uses  to  which  isolated  sections  of  one  species  put 
their  powers,  when  appropriating  resources  from  the  same  environ- 
ment, must  produce  diversity  in  the  forms  of  variation  that  are  most 
successful  in  the  different  sections.  This  I  call  active  selection  as  con- 
trasted with  passive  selection,  which  varies  according  to  differences 
in  the  environments.!  All  diversities  of  environal  selection  that  do 
not  vary  according  to  differences  in  the  environments  must  be  classed 
as  diversities  of  active  selection,  for  they  must  have  originated  in 
some  variation  in  the  powers  of  the  organism  or  in  the  diversity  of 
uses  to  which  it  has  put  its  powers.  Diversity  in  the  successful  use 
of  the  powers  of  the  species  in  dealing  with  the  environment,  whether 

*  To  these  I  now  add  prudential  selection. 

t  For  "active"  and  "passive"  selection,  I  often  substitute  " endonomic "  and 
"heteronomic"  selection. 


198  APPENDIX  II — INTENSIVE   SEGREGATION. 

initiated  by  diversity  in  the  action  of  the  species  in  its  different  sec- 
tions or  by  diversity  in  the  nature  of  the  different  environments, 
necessarily  introduces  diversity  of  environal  selection.  This  principle 
may  be  expressed  as  the  dependence  of  diversity  of  environal  selection 
on  diversity  in  the  relations  of  the  powers  of  the  organism  to  conditions  in 
the  environment. 

(5)  Diversity  of  innate  powers  in  the  different  sections  of  a  species 
can  not  be  maintained  and  accumulated  without  some  degree  of  segre- 
gation between  the  different  sections,  for  within  one  intergenerating 
group  every  initial  divergence  is  speedily  merged  in  the  general  char- 
acter of  the  group.  This  law  may  be  briefly  defined  as  the  depend- 
ence of  increasing  divergence  of  racial  characters  on  the  continuance  of 
isolation.  As  was  shown  in  my  paper  on  "Divergent  Evolution," 
without  the  aid  of  causes  preventing  intercrossing,  the  selection  of 
other  than  average  forms  will  produce  transformation  but  never  diver- 
gence— will  produce  monotypic  but  never  polytypic  evolution. 

(6)  Diversity  in  the  character  of  the  selection  may  be  introduced, 
not  only  by  the  intervention  of  new  forms,  but  also  by  the  cessation 
of  old  forms  of  selection.  We  shall  find  that  important  differences  of 
this  kind  may  arise,  resulting  in  considerable  transformation  before 
any  new  form  of  selection  has  come  into  action.  A  good  illustra- 
tion of  the  cessation  of  selection  is  found  in  the  increasing  frequency 
with  which  human  mothers,  notwithstanding  their  failure  to  give 
suck,  succeed  in  raising  their  children.  The  power  to  give  suck  is 
through  this  process  being  diminished  in  the  more  civilized  races, 
though  there  is  no  reason  to  believe  that  those  who  do  not  give  suck 
have,  on  the  whole,  any  advantage  over  those  who  do.  The  new 
result  is,  therefore,  being  produced  not  by  the  introduction  of  a  new 
form  of  filio-parental  selection,  but  by  the  cessation,  or  the  weaken- 
ing, of  the  old  form.  Romanes  has  pointed  out  the  eflfects  that  must 
often  be  produced  by  the  cessation  of  natural  selection,*  but  he  has 
not  considered  the  cessation  of  other  forms  of  selection.  In  subse- 
quent paragraphs  of  this  section  relating  to  social  and  filio-parental 
selection  are  given  a  number  of  examples  of  the  influence  of  accom- 
modation in  causing  certain  forms  of  selection  to  cease  and  in  certain 
cases  introducing  new  forms  of  selection  that  are  the  reverse  of  the 
older  forms. 

(7)  It  is  often  convenient  to  distinguish  between  selection  resulting 
from  rational  devices  and  that  resulting  from  the  superior  success  of 

♦See  an  article  on  "The  Factors  of  Organic  Evolution,"  in  Nature,  vol. 
XXXVI,  pp.  402-404,  in  which  reference  is  made  to  previous  papers  in  which  the 
cessation  of  natural  selection  is  discussed. 


FORMS  OP  SEI.ECTION. 


199 


organisms  better  adapted  than  their  rivals  of  the  same  intergenerant 
to  the  natural  laws  and  conditions  of  the  environment,  or  to  the  nat- 
ural constitution  of  the  species  to  which  they  belong.  The  former  I 
call  rational  selection  and  the  latter  adaptational  selection.  Under  the 
former  I  place  artificial  [prudential]  and  institutional  selection,  and 
under  the  latter  I  place  processes  as  unlike  as  natural  selection  and 
sexual  selection.  This  classification  does  not,  however,  seem  to  me 
so  important  or  so  fundamental  and  clearly  definable  as  that  which 
rests  on  the  fact  that  some  forms  of  selection  depend  on  the  relations 
in  which  organisms  stand  to  the  environment,  while  others  depend  on 
the  relations  in  which  the  members  of  the  same  species  stand  to  each 
other.  It  may  here  be  noted  that  artificial  selection  is  the  exclusive 
generation  of  those  that  are  better  fitted  to  the  rational  environment, 
through  the  failure  to  propagate  of  those  that  are  less  fitted.  The 
effect  is  the  same  whether  the  failure  to  propagate  is  through  lack  of 
adaptation  to  human  purposes  or  through  lack  of  adaptation  to  the 
unreasoning  environment. 

The  following  table  of  the  forms  of  selection  will,  I  think,  be  a  help  in 
maintaining  these  and  other  distinctions. 

Forms  op  Selection. 


ADAPTATIONAI,  SELECTION. 
Active  (or  endonomic)  selection. 

Habit udinal  selection. 
Aptitudinal  selection. 

Passive  or  keteronomic  selection. 
Natural  selection. 


RATIONAL  SELECTION. 

.  Heteronomic  selection. 
a 
<u 

g  Artificial  selection. 

2 

§  Conscious. 

s 

Unconscious. 


Conjunctional  selection. 

Institutional  selection. 

Sexual  selection. 

Ecclesiastical  selection 

Social  selection. 

Military  selection. 

^ 

•0 
9, 

Filio-parental  selection. 

Sanitary  selection. 

0 

0 
C 

Dominational  selection. 

Penal  selection. 

0 

W 

Prepotential  domination. 

3 

Sustentational  domination. 

> 

T3 

C 
cd 

Protectional  domination. 
Nidificational  domination. 

Prudential  selection. 

01 

Nuptial  domination. 

w 

J2 

Impregnational  selection. 

PP 

Dimensional  selection. 
Structural  selection. 
Potential  selection. 
Fecundal  selection. 

/ 
20O  APPENDIX   II — INTENSIVE   SEGREGATION. 

(9)  Environal  selection. — As  environal  selection  involves  not  only 
the  superior  propagation  of  the  better  fitted,  but  the  inferior  propa- 
gation of  the  less  fitted  and  the  non-propagation  of  the  least  fitted, 
it  may  be  described  as  the  exclusive  propagation  of  those  better  fitted 
to  the  environment  through  the  failure  to  propagate  of  the  less  fitted. 
Transformation  by  means  of  environal  selection  depends  on  the  vary- 
ing degrees  of  adaptation  to  the  environment  in  creatures  that  are  in- 
tergenerating,  the  higher  degrees  being  possessed  by  other  than  aver- 
age forms.  Divergence  is  produced  by  environal  selection  only  when 
to  the  above  conditions  producing  transformation  are  added  causes 
that  prevent  intercrossing  between  the  sections  that  are  being  inde- 
pendently transformed.  In  other  words,  independent  environal  selec- 
tion produces  divergence. 

(10)  Sexual  selection  is  the  exclusive  propagation  of  those  better 
fitted  to  the  sexual  instincts  of  the  species  through  the  failure  to 
propagate  of  the  less  fitted.  In  the  words  of  Darwin,  ' '  It  depends  on 
the  advantage  which  certain  individuals  have  over  others  of  the  same 
sex  and  species  solely  in  respect  of  reproduction."*  It  is  the  form 
of  reflexive  selections  which  has  received  Darwin's  attention,  and  is 
consequently  famiHar  to  all.  There  are,  however,  certain  points  that 
need  to  be  emphasized. 

This  is  the  principle  in  accordance  with  which  correspondence  is 
secured  between  the  external  characters  and  the  sexual  instincts  of  a 
species,  and  also  between  the  instincts  of  the  two  sexes,  in  so  far  as 
they  relate  to  reproduction.  This  result  is  secured  partly  by  the 
failure  to  propagate  of  those  whose  powers  of  attraction  and  conquest 
do  not  reach  the  standard  demanded  by  the  instincts  of  the  other  sex 
and  partly  by  the  failure  of  those  whose  instincts  diverge  too  widely 
from  the  typical  characteristics  of  the  other  sex.  For  example,  on 
the  highlands  of  North  China  I  have  observed  a  species  of  creeping 
cricket  of  the  genus  Bradyphorus,  the  male  of  which  calls  the  female 
by  a  sharp  stridulation,  to  which  the  female  responds  by  approaching 
the  male  and  finally  climbing  upon  its  back.  Now,  we  can  well  under- 
stand that  the  call  of  the  male  has  been  brought  to  its  present  shrill, 
penetrating  perfection  through  the  failure  to  attract  mates  in  the  case 
of  males  that  were  but  feebly  endowed,  but  it  is  equally  certain  tha  . 
those  females  whose  sluggish  instincts  have  been  capable  of  respond- 
ing only  to  an  unusually  intense  call  have  for  the  most  part  failed  of 
leaving  offspring,  and,  if  any  have  been  so  unreasonable  as  to  wait  for 
the  male  to  seek  them  out,  they  have,  doubtless,  perished  without  per- 

*  "Descent  of  Man,"  p.  3  of  Chap.  VIII. 


SNVIRONAL   AND  SEXUAL  SELECTION.  20I 

petuating  their  perverted  instincts.  If  my  view  is  correct,  the  change 
producing  divergent  sexual  characteristics  may  be  either  in  the 
instinct  or  in  the  characters  with  which  the  instinct  is  correlated.  -  It 
seems  probable  that  in  the  vast  majority  of  cases  the  more  strongly 
divergent  forms  have  been  reached  by  a  multitude  of  deviations  alter- 
nating between  the  psychical  and  the  physiological  and  morphological 
characters  of  the  species,  the  chief,  indispensable  condition  being  the 
prevention  of  interbreeding  between  the  diverging  sections  of  the 
species. 

Sexual  selection  is  sometimes  referred  to  as  if  it  were  the  influence 
of  sexual  instincts  in  giving  character  to  the  organs  of  a  given  sex, 
first  by  the  instincts  of  the  given  sex  rousing  the  individuals  of  that 
sex  to  successful  activity  in  securing  propagation,  the  degree  of  suc- 
cess depending  on  the  degree  of  adaptation  of  the  organs  of  the  indi- 
vidual to  the  purpose  of  the  activity  (as  in  the  case  of  barnyard  cocks 
winning  partners  by  the  use  of  their  spurs),  and,  second,  by  the  in- 
stincts of  the  opposite  sex  being  roused  to  successful  action  according 
as  the  endowments  of  the  given  sex  are  fitted  to  the  end  (as  in  the 
case  of  peacocks  winning  partners  by  the  display  of  ornamentation) . 
Starting,  however,  with  this  conception  of  the  nature  of  sexual  selec- 
tion, we  shall  find  great  difficulty  in  obtaining  from  the  principle 
any  explanation  of  the  origin  of  species  or  of  divergent  evolution  of 
any  kind.  If  divergent  instincts  are  the  causes  of  divergent  forms, 
colors  and  qualities,  what  are  the  causes  of  the  transformation  of  the 
instincts  in  lines  that  are  persistently  divergent?  The  problems  of 
transformation  and  divergence  are  as  far  from  solution  after  the  appli- 
cation of  the  theory  as  before. 

If,  on  the  other  hand,  we  recognize  sexual  selection  as  the  har- 
monizing of  the  forms,  colors,  and  qualities  of  a  species  with  its  sexual 
instincts  and  of  the  sexual  instincts  with  its  forms,  colors,  and  quali- 
ties, we  shall  not  claim  that  either  set  of  characters  is  directly  and 
continuously  the  cause  of  transformation  in  the  other;  but  rather 
that  the  two  sets  play  upon  each  other  in  such  a  way  as  to  produce  a 
state  of  unstable  equilibrium  in  both  sets,  the  result  of  which  is  indefi- 
nite transformation  in  the  secondary  sexual  characters  of  each  section 
of  a  species  that  constitutes  a  separate  intergenerant,  and  that  the 
independent  transformation  inevitably  results  in  divergence.  In 
Darwin's  presentation  of  the  principle  of  sexual  selection,  the  chief 
endeavor  is  to  show  that  differences  in  voice  and  ornamentation 
between  males  and  females  of  the  same  species  are  probably,  in  a  large 
degree,  due  to  diversity  in  the  action  of  sexual  selection  upon  the 
different  sexes ;  but  this  is  a  very  different  result  from  differences  in 


202  APPENDIX  II — INTENSIVE   SEGREGATION. 

the  same  respects  between  those  of  the  same  sex  in  closely  allied  varie- 
ties and  species,  and  no  clear  understanding  of  the  subject  will  ever 
be  reached  till  those  who  study  and  discuss  the  subject  discriminate 
between  these  two  classes  of  phenomena.  The  formation  of  differ- 
ences of  the  former  kind  is  simple  transformation  without  divergence, 
while  the  entrance  of  differences  of  the  latter  kind  is  divergent  evolu- 
tion tending  to  the  production  of  separate  species. 

If  a  species  deficient  in  secondary  sexual  distinctions,  after  being 
divided  into  segregated  sections,  attains  a  high  development  of  such 
distinctions,  it  is  easy  to  believe  that  they  will  be  developed  in  differ- 
ent ways  in  the  different  sections,  and  that  thus  they  will  become 
specific  distinctions ;  but  it  is  not  so  easy  to  see  why  a  species  in  which 
sexual  distinctions  have  already  been  fully  developed  should  undergo 
divergent  changes  in  the  different  sections  into  which  it  may  be 
divided.  It  is  in  such  cases  that  we  discover  the  important  influence 
of  what  I  have  called  unstable  equilibrium.  It  seems  probable  that  in 
some  cases  small  differences  originating  through  indefinite  variation 
in  only  a  few  isolated  individuals  are  seized  upon  by  the  exaggerating 
fancies  of  the  other  sex,  and  are  thus  first  preserved  through  isolation 
and  then  exaggerated  by  sexual  selection.  In  other  words,  indepen- 
dent sexual  selection  produces  segregation  and  divergence. 

(ii)  Social  selection  is  the  exclusive  breeding  of  those  better  fitted 
to  the  social  constitution  and  instincts  of  the  race  through  the  failure 
to  breed  of  those  less  fitted.  Social  organization  -has  reference 
chiefly  to  cooperation  in  securing  sustentation  and  defense.  If  for 
each  species  there  were  but  one  possible  form  of  social  organization 
through  which  sustentation  could  be  secured,  there  would  be  no  need 
of  considering  social  selection,  for  the  form  of  social  organization 
would  be  rigorously  determined  by  natural  selection,  and  the  success 
of  the  individual  through  conformity  to  that  organization  would  be 
sufficiently  explained  by  the  principle  of  natural  selection.  But  dif- 
ferent forms  of  social  organization  are  often  exhibited  by  the  same  or 
closely  allied  species ;  and  we  find  that,  in  such  cases  as  elsewhere,  the 
prosperity  of  the  individual  is  largely  dependent  on  his  conformity  to 
the  social  organism  to  which  he  belongs.  Social  selection  must,  there- 
fore, in  some  cases,  have  been  an  important  factor  in  maintaining  a 
correspondence  between  the  capacities  and  the  social  organization  of  a 
race  or  species.  When  a  species  or  a  section  of  a  species  is  undergoing 
a  change  of  social  habits,  there  will  be  individuals  that  fail  through 
reverting  to  the  old  instincts  and  methods  which  put  them  out  of 
accord  with  the  rest  of  the  community.  But  through  the  failure  of 
these  thejnherited  instincts  of  the  race  are  brought  into  increasing 


SOCIAL,   AND   IflLIO-PARENTAlv  SELECTION.  203 

accord  with  the  new  habits  till,  in  the  case  of  most  species,  there  are 
but  few  individuals  that  fail  through  lack  of  appropriate  social  in- 
stincts. Nevertheless,  in  the  branches  of  the  human  species  that  have 
attained  the  highest  civilization  the  process  is  still  far  from  complete, 
for  the  instincts  of  many  individuals  are  in  conflict  with  civilized 
habits. 

We  find  that  the  natural  faculties  that  are  best  fitted  to  secure  indi- 
vidual success,  and  a  numerous  and  long-continued  descent,  are 
different  under  different  forms  of  civilization.  Social  habits  in  a 
great  measure  determine  the  food  and  clothing  of  a  community  and 
thus  deeply  affect  the  qualities  of  the  race.  The  degree  of  exposure 
to  which  the  young  are  habitually  subjected  is  also  largely  determined 
by  social  custom,  and  so  the  quality  of  the  constitution  that  is  per- 
mitted to  survive.  In  other  words,  the  form  of  parental  selection 
that  prevails  in  any  community  is  often  determined  by  social  selec- 
tion, as  the  form  of  social  selection  is  sometimes  determined  by  nat- 
ural selection.  Many  matters  which,  amongst  irrational  animals, 
are  determined  by  instincts  guiding  the  individual  directly  to  the 
needed  resources,  and  showing  what  provision  must  be  made,  are, 
with  man,  determined  by  social  instincts,  leading  the  individual  to 
follow  the  general  experience  or  traditional  habits  of  his  clan. 

As  in  countries  where  there  are  no  beasts  of  prey  the  gregarious  in- 
stinct of  cattle  ceases  to  be  a  necessity  for  the  preservation  of  life,  it 
is  no  longer  maintained  by  natural  selection,  but  it  may  be  preserved 
by  social  selection ;  for  though  occasional  stragglers  appear,  they  are, 
through  lack  of  adaptation  to  the  social  organization,  specially  liable 
to  fail  of  finding  mates,  and,  therefore,  to  fail  of  propagating  their  kind. 
Between  the  capacities  of  a  community  and  its  social  organization 
there  is  a  constant  action  and  reaction  which  tends  with  more  or  less 
rapidity  toward  transformation ;  and  this  tendency  is  increased  when 
a  small  community,  during  a  long  separation  from  other  communities, 
gradually  increases  in  strength,  independently  constructing  a  civili- 
zation of  its  own.  In  other  words,  independent  social  selection  tends 
toward  divergent  evolution  of  capacities  and  of  social  organization. 

(12)  Filio- parental  selection  is  the  exclusive  breeding  of  those 
better  adapted  to  the  relations  in  which  parents  and  offspring  stand 
to  each  other,  through  the  failure  to  live  and  propagate  of  those  less 
adapted.  How  the  power  of  giving  suck  and  the  corresponding  instinct 
for  sucking  were  first  developed  it  may  be  impossible  to  tell ;  but  it  is 
evident  that  having  once  been  estabhshed  as  the  method  of  sustenta- 
tion  for  the  young  of  mammals,  any  young  lacking  the  instinct  would 
perish  without  leaving  descent.     There  is  every  reason  to  believe  that, 


204  APPENDIX   II — INTENSIVE   SEGREGATION. 

with  the  exception  of  a  few  of  mankind,  and  still  fewer  of  domestic 
animals,  it  may  be  truly  said  of  every  individual  mammal  that  all  its 
ancestry,  through  all  generations  since  they  became  fairly  mammalian, 
have  had  this  instinct  in  full  force ;  and  yet  it  sometimes  fails  and  the 
line  of  descent  is  cut  short  with  the  individual  that  fails.  Till  compara- 
tively recent  times  the  same  was  true  of  man ;  but  we  now  find  some 
cases  in  which  the  young  survive  in  spite  of  their  inability  to  suck, 
and  the  constancy  of  this  mammalian  characteristic  is  being  gradually 
impaired.  There  is  also  in  some  races  an  increasing  tendency  to 
shorter  periods  of  lactation,  of  to  the  entire  suppression  of  the  func- 
tion; so  that  it  seems  not  improbable  that  there  may  yet  arise  a 
variety  of  the  human  species  in  which  the  power  will  be  comparatively 
obsolete.  Under  such  conditions  the  instinct  for  sucking  would  cease 
to  be  of  any  advantage,  while  special  advantage  would  accrue  to  those 
best  able  to  thrive  on  the  artificial  food  habitually  provided  by  the 
parents.  In  some  countries  this  would  be  the  milk  of  ruminating 
animals,  while  in  other  countries  it  would  be  some  vegetable  prepara- 
tion. Through  this  diversity  in  the  food  provided  by  the  parents  for 
their  infants  and  small  children,  there  is  even  now  a  constant  diversity 
in  the  parental  selection  prevailing  in  different  countries.  Diversity 
in  the  forms  of  parental  selection  is  also  produced  by  diversity  in  the 
clothing  and  artificial  heat  provided  by  parents ;  in  the  protection,  on 
the  one  hand,  of  children  from  the  wind  and  rain  and  direct  rays  of  the 
sun,  and  on  the  other  hand,  their  exposure  to  the  same  with  shaven 
heads  or  naked  bodies;  and  in  the  methods  of  binding,  cramping,  and 
mutilating  the  head,  feet,  waist,  and  other  parts  of  the  body.  From 
this  point  of  view  we  see  how  largely  the  form  of  parental  selection  is 
determined  by  social  custom,  and  how  it  is  sometimes  enforced  by 
social  selection,  which  excludes  from  the  benefits  of  the  caste  or  tribe 
all  who  have  not  passed  through  the  ordeal. 

As  filio-parental  selection  is  due  to  diiferent  degrees  of  adaptation 
between  the  parent  and  offspring,  it  may  be  characterized  not  only  by 
fatal  departures  in  offspring  from  the  characters  required  in  their  rela- 
tions to  their  parents,  but  by  fatal  departures  in  parents  from  the  char- 
acters required  in  parents  in  their  relations  to  their  offspring.  As  an 
example  of  the  former,  we  may  refer  to  the  death  at  birth  of  children 
with  excessively  large  heads ;  and  as  an  example  of  the  latter,  to  the 
death  at  birth  of  all  the  children  of  a  mother  with  a  contracted  pelvis. 

(13)  Dominational  selection. — Variations  that  are  equally  fitted  to 
cope  with  the  environment  may  be  divided  into  two  classes — those 
better  able  and  those  less  able  to  cope  with  other  members  of  the 
species  in  the  appropriation  of  resources.     Increase  of  population  and 


DOMINATIONAL   SELECTION,  205 

the  consequent  competition  between  members  of  the  same  species 
condemns  the  latter  to  premature  death,  or  at  least  to  failure  in  prop- 
agating, unless  they  find  new  resources  by  migrating  or  by  changing 
their  habits.  Competition  between  kindred  for  the  possession  of 
identical  resources  we  find  directly  connected  with  two  quite  distinct 
principles  of  evolution :  ( i )  With  the  principle  of  dominational  selec- 
tion tending  to  discriminate  between  those  equally  adapted  to  the 
environment,  through  the  success  and  consequent  propagation  of 
those  only  that  are  best  able  to  cope  with  their  kindred  in  appro- 
priating advantages ;  (2)  with  the  principle  of  competitive  disruption, 
tending  to  break  up  old  relations  and  old  habits,  and  so  preparing 
the  way  for  the  formation  of  new  habits  producing  segregation  and 
divergence.  The  latter  of  these  principles  was  referred  to  at  the 
end  of  Section  III  of  my  paper  on  "Divergent  Evolution  through 
Cumulative  Segregation."  The  first  I  now  briefly  describe,  without 
attempting  to  show  its  important  influence  on  the  transformation 
and  divergence  of  species. 

Dominational  selection  is  the  exclusive  breeding  of  those  better  able 
to  appropriate  natural  resources  or  mates,  or  the  provision  made  by 
parents  of  society,  not  through  being  better  fitted  to  the  environment 
or  to  the  organized  methods  of  cooperation  and  assistance,  but  through 
being  better  able  to  overcome  or  outdo  their  rivals  of  the  same  species. 
It  results  from  the  contest  or  rivalry  with  each  other  of  members  of  the 
same  species  that  are  equally  fitted  to  the  environment  and  to  the  con- 
stitution of  the  species  and  the  consequent  failure  of  all  that  are  not 
able  to  cope  with  their  kindred.  '  'The  law  of  battle  "  is  a  form  of  dom- 
inational selection  which  Darwin  emphasizes  as  having  great  influence 
in  determining  what  males  shall  have  the  best  success  in  procuring 
mates.  But  there  is  a  similar  law  determining  what  individuals  shall 
obtain  the  resources  furnished  by  nature  or  elaborated  by  parents 
and  society.  We  may  have  dominational  selection  relating  to  susten- 
tation,  protection,  and  nidification,  as  well  as  to  the  possession  of 
females.  And  in  gaining  a  single  end  there  may  be  a  great  variety 
of  dominating  methods.  Combat  between  males  for  the  possession  of 
females  is  not  found  in  the  vegetable  kingdom ;  but  the  prepotence  of 
the  pollen  of  certain  flowers  over  that  of  other  flowers  of  the  same  race 
may  play  a  similar  r61e.     This  we  may  call  prepotential  domination. 

Dominational  selection  differs  from  natural  selection  in  that  it  does 
not  depend  on  degrees  of  adaptation  to  the  environment,  and  from 
other  forms  of  reflexive  selection  in  that  it  depends  on  a  special  form 
of  the  relationship  in  which  members  of  the  same  species  stand  to  each 
other.     It  seems  desirable  that  this  form  of  selection,  which  depends 


206  APPENDIX   II — INTENSIVE   SEGREGATION. 

on  adaptation  for  overcoming,  outdoing,  or  supplanting  others  of  the 
same  species,  should  be  clearly  distinguished  and  named.  We  further 
note  that  there  can  be  no  doubt  that  dominational  selection  acting 
for  many  generations  on  sections  of  a  species  that  are  prevented  from 
intercrossing  will  in  all  probability  follow  somewhat  different  lines. 
In  other  words,  independent  dominational  selection  will  produce  diver- 
gent evolution. 

(14)  *  Impregnational  selection. — The  coordination  between  the  pollen  of  a 
given  species  and  the  stigma  and  ovules  of  the  same  species  must  be  kept  up  by  a 
process  of  selection,  resulting  from  the  failure  to  propagate  of  the  individuals  whose 
pollen  is  least  potent,  and  of  those  whose  ovules  are  most  difficult  to  fertiUze. 
This  we  may  appropriately  call  potential  selection;  and  it  will  be  convenient  to 
class  it  with  forms  of  selection  securing  other  coordinations  necessary  for  success- 
ful impregnation.  These  other  forms  are:  dimensional  selection,  of  which  we 
have  an  example  in  the  coordination  between  the  length  of  the  pollen  tubes  and 
of  the  pistils;  also  fecundal  selection,  illustrated  by  the  different  degrees  of 
survival  secured  by  variation  in  the  number  of  the  ovules  and  in  the  quantity  and 
methods  of  distribution  of  the  pollen  grains;  and,  as  illustrated,  in  many  species 
of  insects,  structural  selection,  due  to  the  success  gained  through  superior  coordi- 
nation of  the  organs  by  which  males  and  females  clasp  each  other.  Impregnational 
selection  is  an  important  form  of  reflexive  selection.  I  wish  here  to  call  especial 
attention  to  the  importance  of  fecundal  selection. 

(15)  Fecundal  selection  produces  intensive  segregation  with  diver- 
gence through  independent  fecundal  intension,  in  isolated  sections  of 
a  species.  It  is  the  form  of  selection  that  results  from  propagation 
according  to  degrees  of  fertility.  As  it  involves  not  only  the  superior 
propagation  of  the  more  fertile,  but  the  inferior  propagation  of  the 
less  fertile  and  the  non-propagation  of  the  least  fertile,  it  may  be 
described  as  the  exclusive  propagation  of  the  more  fertile  through 
the  failure  to  propagate  of  the  less  fertile.  It  would  avail  nothing  in 
determining  the  form  that  is  to  prevail  in  succeeding  generations  if  it 
did  not  in  some  degree  preclude  the  crossing  of  the  less  fertile  with  the 
more  fertile ;  but,  as  it  is  evident  that,  so  long  as  increased  fertility  is 
not  a  disadvantage,  the  more  fertile  half  of  the  species  will  leave  a  larger 
number  of  offspring  than  the  less  fertile  half,  it  follows  that  when  the  off- 
spring have  come  to  maturity  a  larger  portion  of  the  fertile  will  consort 
with  the  fertile  than  in  the  previous  generation ;  and  so  the  fertility  of 
the  following  generation  will  be  still  further  increased.  The  chief  check 
to  this  law  of  cumulative  fertility  is  found  in  the  correlative  law  of 
cumulative  adaptation  through  adaptational  selection.  The  combined 
action  of  these  two  laws  results  in  the  triumphant  development  of  the  most 
fertile  of  the  best  fitted  or  the  best  fitted  of  the  most  fertile. 


♦As  this  paragraph  does  not  occur   in    the    original   paper  it  is  printed  in 
different  form. 


FECUNDAL  AND  INSTITUTIONAL  SELECTION.  207 

Another  result  from  the  combined  action  of  these  two  laws  is  that, 
in  species  well  adjusted  to  the  environment,  the  typical,  that  is  the  average, 
form  of  the  species  is  not  only  the  best  adapted,  but  it  is  the  most  fertile; 
and  this  correlation  between  fertility  and  adaptation  in  the  average 
form  of  the  species  or  race  is  a  strongly  conservative  principle,  tending 
to  prevent  the  rapid  transformation  of  the  race  or  species.  Giants, 
dwarfs,  and  extreme  departures  from  the  type  of  other  kinds  are  more 
likely  to  be  sterile  than  the  typical  form  of  the  species ;  and  therefore 
if,  through  change  in  the  environment  or  in  the  social  conditions,  some 
extreme  form  has  an  advantage  in  gaining  subsistence,  it  will  usually 
fail  of  propagating  its  kind  with  the  relative  rapidity  of  the  less-favored 
average  form.  This  is  at  present  true  of  highly  intellectual  variations 
of  civilized  man.  Those  of  moderate  capacities  are  more  prolific  and 
accordingly  persist,  though  less  successful  in  other  respects  than  the 
intellectual.  But  so  long  as  the  most  successful  individuals  are  those 
surpassing  the  average  in  intellectual  endowment,  so  long  will  the  aver- 
age endowment  be  more  or  less  steadily  advancing ;  for,  of  intellectual 
families,  those  that  are  fairly  fertile  will  leave  more  impress  on  succeed- 
ing generations  than  those  that  are  sterile ;  and  of  fertile  families,  those 
that  are  above  the  average  in  intellect  will  have  the  advantage  in  leav- 
ing descendants  to  inherit  their  endowments. 

( 1 6)  Institutional  selection  is  a  form  of  exclusive  breeding  closely  re- 
lated to  social  selection,  but  differing  from  it  very  much  as  artificial 
selection  differs  from  natural  selection.  Institutional  selection  is 
the  influence  of  institutions,  customs,  and  laws  in  determining  what 
classes  of  individuals  have  an  opportunity  to  raise  children.  In  most 
civilized  countries  criminals  convicted  of  important  offenses  are 
usually  so  confined  as  to  prevent  their  adding  to  the  population  of  the 
community  during  the  time  of  their  confinement.  This  is  a  method 
of  improving  the  race  that  might  be  carried  farther  than  it  has  been. 
In  some  countries  the  insane,  the  imbecile,  and  lepers  are  confined  in 
asylums  and  not  allowed  to  marry,  and  in  other  countries  eccle- 
siastical and  military  restrictions  prevent  certain  portions  of  the 
community  from  raising  families. 

(17)  *  Prudential  selection  is  due  to  the  delay  of  marriage  and  other  methods 
of  limiting  the  number  of  children  for  prudential  reasons. 

(18)  Result  of  the  foregoing  survey  of  selectional  intension. — The  analy- 
sis we  have  now  completed  shows  us  that  certain  changes  in  the  form 
of  selection  are  due  to  changes  in  the  environment  and  that  others  are 


*As  section  (17)  does  not  occur  in  the  original  paper,  it  is  printed  in  different 
form. 


2o8  APPENDIX  11 — INTENSIVE   SEGREGATION. 

due  to  changes  in  the  organism.  We  find :  First,  that  all  the  forms 
of  reflexive  selection  are  due  to  the  relations  of  members  of  the  same 
species  to  each  other,  and  are  liable  to  change  without  any  change  in 
the  environments ;  second,  that  active  selection  is  due  to  change  in 
the  successful  use  of  the  powers  of  the  organism  in  dealing  with  the 
environment  and  is  not  dependent  on  change  in  the  environment; 
third,  that  passive  selection,  which  is  due  to  the  exposure  of  the  or- 
ganism to  a  different  environment,  is  often  produced  by  the  organism's 
entering  a  new  environment  without  there  being  any  change  in  either 
the  new  or  the  old  environment ;  fourth,  that  though  passive  selec- 
tion is  produced  by  change  in  the  environment,  the  more  effective 
forms  of  selection  do  not  appear  till  the  organism  has  so  multiplied  as 
to  produce  what  T  call  " dominational  selection"  through  intense  com- 
petition between  rival  individuals  of  the  same  species  in  gaining  pos- 
session of  limited  resources ;  and  fifth,  that  passive  selection,  which 
depends  on  change  in  the  environment,  also  depends  on  variations  in 
the  adaptations  of  the  organism. 

(19)  *In  this  enumeration  of  the  different  forms  of  selection  I  have  introduced 
certain  divisions  that  are  not  given  in  the  paper  as  read  before  the  Linnean 
Society  in  1889.  These  are  structural,  dimensional,  and  potential  selection 
(which  I  have  grouped  with  fecundal  selection  as  forms  of  impregnational  selec- 
tion), and  prudential  selection,  which  stands  by  itself;  fecundal  selection  was 
discussed  in  the  paper  as  originally  pubUshed,  under  the  term  "fecundal  inten- 
sion." As  having  an  influence  on  survival,  I  now  recognize  it  as  belonging  among 
the  forms  of  selection.  The  active  principle  may  appropriately  be  called  fecundal 
selection,  and  the  effect  it  produces  on  an  organic  group  may  be  called  fecundal 
intension. 

In  preparing  my  table  of  the  forms  of  selection  I  have  found  difficulty  in  decid- 
ing where  natural  selection  should  be  placed,  and  how  wide  a  definition  should  be 
given  to  it.  Some  biologists  use  it  as  including  sexual  selection,  while  others  agree 
with  Darwin  in  considering  sexual  selection  as  belonging  to  a  very  different  sphere, 
seeing  that  changes  in  sexual  selection  depend  on  changes  in  the  activities  of  the 
organism  and  not  on  changes  in  the  environment.  But  appeal  to  Darwin's 
writings  does  not  remove  all  difficulty;  for,  if  we  decide  that  Darwin  does  not 
include  sexual  selection  under  natural  selection,  it  still  seems  certain  that  he 
considered  certain  forms  of  what  I  have  called  dorninational  selection  as  forms  of 
natural  selection.  But  dominational  selection  is  as  decidedly  reflexive  in  its 
action  as  is  sexual  selection.  If,  then,  sexual  selection  is  separated  from  natural 
selection,  should  not  dominational  selection  also  be  considered  as  distinct? 

As  Darwin  has  in  several  places  stated  that  natural  selection  is  subject  to  change 
only  when  external  conditions  change,  f  I  have  classed  it  as  that  form  of  environal 


*As  section  (19)  does  not  occur  in  the  original  paper,  it  is  printed  in  different 
form. 

t  See  Origin  of  Species,  in  the  two  chapters  on  geographical  distribution,  ed.  6, 
especially  on  page  355,  where  Darwin  discusses  the  divergence  of  closely  allied 
species  on  islands  within  sight  of  each  other. 


INDISCRIMINATE   ELIMINATION.  i09 

selection  which  is  controlled  by  activities  belonging  to  natvire  outside  of  the 
species.  It  is,  therefore,  clearly  distinguished  from  active  (or  endonomic)  selec- 
tion, which  is  controlled  by  differences  of  aptitudes  or  of  habitudes  in  the  different 
groups  for  dealing  with  the  environment,  and  not  by  exposure  of  the  different 
groups  to  different  environments. 

9.  Indiscriminate  Eliminalional  Intension. 

Eliminational  intension  is  segregation  and  divergence  produced  by 
the  indiscriminate  destruction  or  failure  to  propagate  of  a  part  of  the 
individuals  of  an  intergenerating  section  of  a  species.  Though  indis- 
criminate destruction  can  not  be  classed  as  a  form  of  natural  selection, 
it  may  nevertheless  be  the  cause  of  transformation ;  and  when  a  species 
is  distributed  in  sections  that  are  prevented  from  intergenerating, 
divergent  evolution  will  often  be  hastened  by  the  indiscriminate 
destruction  of  part  of  the  members  of  one  or  more  sections.  If  a  species 
inhabiting  a  large  island  is  divided  by  geological  subsidence  into  two 
large  sections,  there  may  be  a  very  close  resemblance  in  the  average 
character  of  the  two  sections ;  but  if  a  subsequent  eruption  of  hot  ashes 
destroys  a  large  portion  of  the  individuals  of  one  section,  or  of  both,  the 
probability  of  a  close  correspondence  in  the  average  character  of  the 
two  sections  will  be  very  much  less  than  before  the  eruption. 

Again,  when  the  area  occupied  by  a  species  is  divided  into  two  or 
more  large  districts,  the  occupants  of  which  can  have  little  or  no 
opportunity  for  crossing,  divergent  evolution  will  arise  in  the  different 
districts  unless  there  is  some  constantly  operating  cause  that  insures 
that  all  the  varieties  surviving  and  propagating  in  any  one  district  shall 
survive  and  propagate  in  all  the  districts.  No  such  cause  has  ever  been 
pointed  out,  but,  on  the  contrary,  it  can  easily  be  shown  that  the  prob- 
ability is  very  small  that  such  a  correspondence  would  occur,  even  if 
at  the  time  of  the  division  of  the  areas  every  individual  in  each  district 
was  represented  by  a  completely  similar  individual  in  each  of  the 
other  districts.     Let  us  suppose  a  case : 

(i)  Suppose  the  creatures  under  consideration  to  be  a  species  of 
mollusk,  the  sexual  instincts  of  which  act  without  any  segregative 
tendency  between  the  varieties  of  the  same  species,  there  being  no 
aversion  or  other  impediment  that  interferes  with  the  free  crossing 
of  all  the  variations  occurring  within  the  limits  of  one  district. 

(2)  Suppose  that  the  number  of  individuals  in  each  district  is 
10,000,000. 

(3)  Suppose  that  one  in  a  thousand  of  these  has  a  tongue  strong 
enough  to  feed  on  the  bark  of  the  tree  the  leaves  of  which  are  the  ordi- 
nary food  of  the  species,  and  that  one  in  a  thousand  is  capable  of 


2IO  APPENDIX  II — INTENSIVE  SEGREGATION. 

digesting  the  same,  so  that,  in  each  district  ahke,  one  in  a  million  could 
survive  in  this  way  though  the  crop  of  leaves  should  fail. 

(4)  Suppose  that  there  are,  through  diversity  of  adaptations  of  this 
kind  to  products  of  the  environment,  ten  different  kinds  of  accessible 
forms  of  food,  on  each  kind  of  which  one  in  a  million  of  the  individuals 
of  each  district  might  feed  if  driven  by  necessity. 

(5)  Now  suppose  the  same  necessity  should  occur  in  each  district 
through  the  destruction  of  the  leaves  on  which  they  habitually  feed, 
and  that  there  are  accordingly  in  each  district  a  hundred  survivors 
able  to  maintain  themselves  on  other  kinds  of  food. 

Under  such  circumstances  (the  correspondences  of  which  we  have  in 
our  supposition  made  much  more  exact  than  the  actual  deviations  from 
a  mean  ever  present),  even  under  such  circumstances  of  completely 
parallel  variation,  what  is  the  probability  that  in  each  of  the  separate 
districts  the  few  that  would  meet  with  other  individuals  and  have  an 
opportunity  to  propagate  the  species  would  be  similarly  endowed  and 
similarly  related  to  the  environment  ? 

In  order  to  still  further  simplify  the  problem,  let  us  assume  that  in 
the  case  of  each  kind  in  each  district  the  probability  that  it  will  suc- 
ceed in  propagating  is  exactly  balanced  by  the  probability  that  it  will 
fail.  The  probability,  then,  that  any  given  number,  a,  of  the  ten  kinds 
in  a  given  district  will  succeed  is  found  by  estimating  the  number  of 
ways  in  which  a  things  can  be  taken  out  of  10  things,  and  dividing 
this  number  by  the  tenth  power  of  2,  that  is,  by  1024.  This  is  com- 
pletely parallel  to  the  number  of  ways  in  which  ten  pennies  can  be 
arranged  as  to  head  and  tail,  each  penny  representing  one  form  of  varia- 
tion, and  its  lying  head-up  indicating  success  in  propagating.  In  1024 
experiments  the  probability  is— 


That  6  will  succeed 210  times 

That  7  will  succeed 1 20  times 

That  8  will  succeed 45  times 

That  9  will  succeed 10  times 

That  10  will  succeed i  time 


That  o  will  succeed i  time 

That  I  will  succeed 10  times 

That  2  will  succeed 45  times 

That  3  will  succeed 120  times 

That  4  will  succeed 210  times 

That  5  will  succeed 252  times 

These  figures  are  found  in  the  eleventh  line  of  what  is  known  as  the 
' '  Table  of  the  Binomial  Coefficients, "  or  the  "  Arithmetical  Triangle. ' '  * 
And  so  in  the  case  of  any  number  of  objects,  the  number  of  combina- 
tions that  may  be  made  with  n  objects  is  found  in  the  w  +  ith  line  of 
the  arithmetical  triangle  classified  according  as  there  are  o,  1,2,  3,  or 
more  objects  in  each  combination.  The  whole  number  of  combina- 
tions may  also  be  found  by  calculating  the  nth.  power  of  2. 

*  See  "Principles  of  Science,"  by  W  S.  Jevons. 


AMALGAMATIONAL  INTENSION.  211 

The  possible  combinations  of  the  ten  varieties  in  question,  any  one 
of  which  is  as  Ukely  to  occur  as  is  any  other,  are  1,024,  which  is  equal 
to  2  raised  to  the  loth  power;  the  probability,  therefore,  that  the  com- 
bination or  set  of  varieties  that  succeeds  in  one  district  is  j^,  or  i  in 
1,024 ;  while  the  probability  that  those  that  succeed  in  the  one  district 
will  not  be  all  the  same  as  in  the  other  will  be  j^,  or  1,023  in  1,024, 
which  is  more  than  a  thousand  times  greater  than  the  reverse  prob- 
ability. 

These  1,024  different  results,  any  one  of  which  may  occur  in  one 
section,  are  calculated  on  the  supposition  that  all  the  representatives 
of  the  species  in  one  section  that  succeed  in  propagating  will  in  time 
coalesce  by  intercrossing;  as  we  shall  presently  see,  the  number  of 
divergences  in  the  two  sections  may  be  vastly  increased  by  the  diver- 
sity of  ways  in  which  the  same  varieties  may  be  combined  through  the 
greater  or  less  influence  of  minor  segregations  within  the  bounds  of 
each  district. 

10.  Amalgamational  Intension. 

In  my  paper  on  ' '  Divergent  Evolution  through  Cumulative  Segre- 
gation," I  have  referred  to  the  fact  that  the  vast  majority  of  diver- 
gent forms  produced  by  segregation,  after  existing  for  a  time,  are 
interfused  with  competing  forms  of  the  same  species.  Now,  it  is 
evident  that  when  a  permanent  segregation  arises,  if  in  the  separate 
sections  there  is  a  diversity  of  amalgamations  between  the  slightly 
divergent  forms  produced  by  partial  segregations,  the  results  will  be 
divergent  in  these  separate  sections.  That  there  will  be  diversity  in 
this  respect,  we  may  argue,  first,  from  the  improbability  that  all  the 
varieties  in  any  one  section  will  occur  in  each  of  the  other  sections; 
Second,  from  the  improbability  that  if  the  same  varieties  occur  in  each 
section  they  will  occur  in  the  same  proportions ;  and,  third,  from  the 
improbability  that  if  they  are  the  same  and  in  the  same  proportions, 
they  will  break  over  the  barriers  and  breed  with  each  other  in 
precisely  the  same  way  in  each  section.  Amalgamational  intension 
relates  only  to  the  last  point.  The  other  two  points  have  been  dis- 
cussed under  the  principle  that  separation  always  involves  more  or 
less  segregation  (see  the  third  paragraph  on  the  first  page  of  this 
paper),  and  under  indiscriminate  elimination,  which  we  have  just  been 
considering. 

Taking  up,  again,  the  supposed  case  considered  under  eliminational 
intension,  if  the  different  kinds  of  new  food  were  so  situated  as  to 
make  it  more  or  less  difficult  for  those  feeding  on  one  kind  to  cross 
with  those  feeding  on  other  kinds,  the  representatives  of  the  species  in 
each  of  the  completely  separated  districts  would  be  divided  into  minor 


212  APPENDIX  II — INTENSIVE   SEGREGATION. 

segregations  of  a  partial  kind ;  and  the  different  degrees  of  intercross- 
ing between  the  minor  segregations  in  the  separate  districts  would  be 
an  additional  cause  of  divergence,  which  we  may  appropriately  class 
as  a  form  of  amalgamational  intension.  Occasional  interchange  of 
stations  by  the  varieties  in  one  district  would  produce  a  degree  of 
homogeneity  in  the  forms  of  one  district  that  would  not  be  found  when 
comparing  those  of  different  districts;  but  as  the  degrees  of  inter- 
crossing between  any  two  or  more  identical  varieties  that  might 
happen  to  be  preserved  in  both  districts  would,  in  all  probability,  differ 
in  different  districts,  the  correspondence  that  at  first  existed  between 
certain  portions  of  the  two  sections  would  gradually  disappear. 

1 1 .  Combined  Infitience  of  these  Principles. 

We  have  not  at  present  sufficient  knowledge  of  the  influence  of  each 
of  the  principles  of  transformation  to  enable  us  to  estimate  their  com- 
parative importance ;  but  we  know  enough  of  their  combined  action 
to  anticipate  with  confidence  that  wherever  separate  or  segregate 
generation  arises,  producing  more  or  less  divergence,  there  these  prin- 
ciples will  in  time  intensify  the  result.  The  transformations  and 
divergences  of  nature  are  produced  by  the  interplay  of  numerous 
factors  most  intimately  combined,  and  though  for  the  purpose  of  com- 
prehending the  process  we  are  compelled  to  study  each  principle  by 
itself,  we  must  remember  that  in  nature  they  not  only  combine,  but 
combine  in  a  vast  variety  of  ways.  There  is,  however,  reason  to  be- 
lieve that  species  sometimes  become  so  devoid  of  plasticity  that  nearly 
all  transformation  is  precluded,  and,  if  the  environment  is  greatly 
changed,  even  in  the  most  gradual  manner,  extinction  is  the  result. 

II.  Divergence  in  Mollusks. 
1.  Divergent  Evolution  in  the  Land  Mollusks  of  Oahu. 

Oahu  is  one  of  the  Sandwich  Islands,  or  Hawaiian  Islands,  as  they 
are  now  usually  called.  It  is  of  volcanic  origin,  but  the  two  mountain 
ranges,  which  lie  one  on  the  northeast  and  the  other  on  the  southwest 
side  of  the  island,  show  no  signs  of  recent  volcanic  action.  Unlike  the 
mountains  of  Hawaii  and  East  Maui,  their  sides  are  very  deeply  fur- 
rowed by  the  action  of  water,  and  their  forests  are  not  broken  by 
flows  of  lava.  The  forests  of  the  islands  cover  these  two  ranges,  form- 
ing two  disconnected  strips,  the  one  about  36  and  the  other  about  1 8 
miles  in  length.  In  these  forests  are  found  many  hundred  varieties^ 
,  representing  over  200  species,  belonging  to  8  genera,  of  the  Achati- 
nellidae. 


LAND   MOlvIvUSKS  OP  OAHU.  213 

Two  of  these  genera,  Araastra  and  Leptachatina,  are,  for  the  most 
part,  found  under  the  dead  leaves  of  trees  in  damp  places;  and  one, 
Ivaminella,  is  found  chiefly  on  low  shrubs,  while  the  remaining  five 
genera  are  always  found  on  trees  or  shrubs.  Now,  it  must  be  remem- 
bered that  the  climate  is  tropical,  and  that  the  rainfall  is  so  distributed 
through  the  year  that  in  the  shady  groves  there  is  nothing  to  drive  the 
arboreal  species  from  their  haunts  on  the  leaves  or  branches  of  the 
trees.  Still  further,  as  this  family,  unlike  most  other  land  mollusks, 
produces  its  young,  not  from  eggs,  but  in  a  living,  active  form,  there  is 
no  occasion  in  its  life  history  that  requires  it  to  leave  the  tree  in  which 
it  lives  from  generation  to  generation.  In  the  distribution  and  diver- 
gence of  these  varieties  and  species  we  learn  the  following  lessons : 

( I )  Varieties  are  incipient  species,  and  species  are  strongly  pronounced 
varieties.  A  full  collection  of  the  varieties  and  species  of  any  poly- 
morphic genus  produces  an  oppressive  sense  of  confusion  on  the  mind 
of  anyone  who  examines  it  for  the  first  time.  This  is  preeminently 
true  of  a  full  collection  of  the  Achatinellidse  of  the  island  of  Oahu. 
Eight  genera  are  represented  by  a  multitude  of  varieties  and  species 
which,  within  the  limits  of  each  genus,  are,  for  the  most  part,  com- 
pletely intergraded  with  each  other.  As  natural  selection  has  not 
removed  the  intermediate  forms,  it  is  impossible  to  say  where  a  species 
begins  and  where  it  ends.  Having  selected  a  given  form  as  the  type 
of  a  given  arboreal  species,  we  soon  find  that  it  inhabits  perhaps  only 
one  or  two  valleys,  say  half  a  mile  in  width,  and  only  one,  two,  or 
three  miles  in  length.  Beyond  these  limits  it  is  represented  by  varie- 
ties that  become  more  divergent  as  the  distance  from  the  home  of  the 
type  increases ;  and,  in  the  case  of  the  Achatinella  and  Bulimella,  this 
difference  is  so  great  that  in  districts  eight  or  ten  miles  apart  every 
one  will  admit  that  the  forms  all  belong  to  different  species.  Indeed, 
in  many  cases,  though  the  same  vegetation  is  present,  the  habits  of 
feeding  have  changed,  while  in  other  cases  the  form  and  color  have 
changed  while  the  habits  remain  essentially  the  same. 

Though  it  is  easy  to  find  degrees  of  divergence  which  most  natu- 
ralists will  agree  in  calling  specific,  but  which  in  a  full  collection  are 
shown  to  be  completely  intergraded,  yet  if  a  full  collection  of  the  dif- 
ferent forms  should  be  submitted  in  succession  to  a  hundred  different 
naturalists  to  classify,  it  would  be  found  that  no  two  would  agree  as 
to  the  number  of  species,  and  a  still  greater  diversity  of  opinion  would 
be  revealed  as  to  where  the  limits  of  the  different  species  should 
be  placed.  This  is  exactly  what  we  might  expect  if  varieties  are 
incipient  species,  and  species  are  simply  strongly  developed  varieties. 
Such  being  the  case,  it  is  folly  to  ask  that  the  nomenclature  should 


214  APPENDIX   II — INTENSIVE^   SEGREGATION. 

be  based  on  some  fundamental  distinction  between  species  and 
varieties.* 

The  best  nomenclature  is  the  one  in  which  the  specific  distinctions 
correspond  in  degree  with  those  that  are  recognized  as  specific  in  other 
families,  and  in  which  a  degree  of  divergence  that  is  considered  specific 
in  one  part  of  a  genus  is  considered  specific  in  every  part.  If  the  dis- 
tinctions on  which  Reeve,  Pfeiffer,  and  Newcomb  have  founded  the 
species  in  Makiki  and  Manoa  are  received  as  specific  distinctions,  then 
similar  distinctions  occurring  in  the  forms  of  other  valleys  must  be 
recognized  as  belonging  to  different  species.  I  by  no  means  contend 
that  these  differences  should  be  regarded  as  specific;  but  having  re- 
ceived the  three  or  four  forms  of  Achatinella  found  in  Manoa  as  good 
species,  it  will  not  do  to  say  that  the  forms  of  Achatinella  found  in 
Waialei,  differing  from  each  other  in  the  same  manner  and  degree, 
are  but  one  species. 

Notwithstanding  the  diversity  of  opinion  that  will  always  exist  as 
to  how  many  species  should  be  made  of  the  forms  occurring  in  any  one 
valley,  every  one  will  agree  that  the  forms  of  Bulimella  and  Achati- 
nella found  in  any  one  valley  are  quite  distinct  species  from  those 
found  in  valleys  that  are  ten  or  twenty  miles  distant.  The  lessons  we 
are  drawing  from  the  divergence  in  this  family  are,  therefore,  not 
dependent  on  any  special  views  concerning  the  number  of  species  that 
ought  to  be  received. 

As  examples  of  intergrading  species,  examine  first  the  types  of 
Achatinella  producta,  A.  adusta,  and  A.  huddii  from  Makiki;  then  all 
the  forms  of  these  and  the  other  species  of  Achatinella  found  in  Ma- 
kiki, and  then  the  forms  found  in  the  successive  valleys  of  the  whole 
mountain  range. 

If  freedom  from  intergrading  is  received  as  the  necessary  and  suf- 
ficient test  of  good  species,  then  a  multitude  of  forms  that  are  only 
varieties  may  be  turned  into  good  species  by  burning  the  forests  in 
alternate  valleys  on  either  side  of  this  mountain  range.  Moreover,  if 
this  is  the  true  test  of  species,  the  species-maker  who  throws  intergrade 
forms  into  the  fire  is  quite  consistent,  even  if  not  quite  frank. 

Whether  we  call  these  divergent  forms  species  or  varieties,  the  pro- 
cess by  which  the  divergence  has  been  produced  is  a  matter  of  equal 
interest.  Indeed,  some  evolutionists  maintain  that  one  of  the  chief 
desiderata  in  the  theory  of  evolution  is  an  explanation  of  the  origin  of 
varieties.!     Variations  are  deviations  from  the  average,  but  varieties 


*So  far  as  the  necessary  material  can  be  obtained  the  statistical  method  of 
testing  species  is  under  such  conditions  the  best. 

t  See  "  Evolution  and  its  Relations  to  Religious  Thought,"  by  Joseph  Le  Conte, 
published  by  Appleton  &  Co.,  p.  252 


DARWIN   AND   SPENCKR  ON   CAUSES  OI^   DIVERGENCE.         215 

are  groups  of  individuals  in  which  the  averages  differ,  and  in  which 
the  inheritable  characters  differ.  Still  further,  it  is  usually  admitted 
that  the  divergences  presented  by  varieties  are  not  always  essential  to 
the  well-being  of  the  forms  that  possess  them,  and  that  in  many  cases 
the  forms  that  are  confined  to  separate  localities  might  exchange  posi- 
tions without  suffering  disadvantage.  Divergence  in  these  initial 
stages  has  seemed  to  many  to  be  an  obscurer  problem  than  the  ad- 
vancing usefulness  which  sometimes  entirely  remodels  an  organ.  For 
as  Professor  Le  Conte  has  said,  ' '  Natural  selection  does  not  make  an 
organ  useful,  but  only  more  useful." 

I  believe  the  theory  of  divergent  evolution,  presented  in  this  and 
the  preceding  paper,  is  applicable  to  the  formation  of  divergences 
during  the  stage  when  some  of  the  differences,  if  not  all,  bring  neither 
advantage  nor  disadvantage  to  those  that  possess  them.  Whatever 
we  call  these  divergent  forms,  can  we  give  any  explanation  of  the 
causes  that  have  produced  them? 

(2)  Divergent  evolution  does  not  necessarily  depend  on  diverse  envi- 
ronments. In  other  words,  it  does  not  necessarily  depend  on  change  in 
the  conditions  surrounding  the  organism,  or  on  the  organism  being 
brought  into  a  district  presenting  a  different  set  of  conditions. 

Darwin  maintains  that  isolation  (by  which  he  designates  geo- 
graphical separation),  without  any  differences  in  the  surrounding 
organisms  or  in  the  physical  conditions,  presents  no  occasion  for 
divergence  of  character.  He  says,  "If  a  number  of  species,  after 
having  long  competed  with  each  other  in  their  old  home,  were  to 
migrate  in  a  body  into  a  new  and  afterwards  isolated  country,  they 
would  be  little  liable  to  modification."     (Origin  of  Species,  6th  ed., 

P-  319) 

Spencer  expresses  the  same  idea  by  saying  that  "Vital  actions 
remain  constant  so  long  as  the  external  actions  to  which  they  corre- 
spond remain  constant."*  There  must  be  maintained  a  tolerably 
uniform  species  so  long  as  there  continues  a  tolerably  uniform  set  of 
conditions  in  which  it  may  exist."  (See  Spencer's  Principles  of 
Biology,  sections  91,  156,  169,  170.)  In  other  words,  divergence  of 
character  in  the  descendants  of  one  stock  occupying  different  districts 
does  not  arise  except  as  it  is  preceded  by  difference  in  the  physical 
conditions,  or  in  the  surrounding  organisms,  of  the  different  districts. 
After  molding  this  thought  in  many  forms,  Spencer  makes  it  the  funda- 
mental principle  on  which  he  builds  not  a  small  portion  of  his  philos- 


*  Though  apparently  opposed  to  his  theory  of  ' '  the  production  of  certain  local 
forms  by  amixia,"  this  same  idea  is  found  in  Weismann's  "Studies  in  the  Theory 
of  Descent,"  pp.  109-115  (English  edition). 


2l6  APPENDIX  II — INTENSIVE   SEGREGATION. 

ophy.  Darwin  is  more  guarded  in  his  statements ;  still,  as  we  have 
already  shown,  he  sometimes  seems  to  reason  from  an  assumption  quite 
in  accord  with  what  Spencer  would  have  us  receive  as  essential  to  the 
very  idea  of  causation  in  vital  processes.  For  example,  his  explanation 
of  the  fact  that  on  the  different  islands  of  the  Galapagos  Archipelago 
one  genus  is,  in  many  cases,  represented  by  several  closely  allied 
species  which  are  undoubtedly  modified  forms  of  one  continental 
species,  seems  to  rest  on  the  assumption  that  if  every  species  that 
gained  access  to  any  island  had  at  the  same  time  gained  access  to  the 
other  islands  of  the  archipelago,  there  would  then  have  been  no  occa- 
sion or  opportunity  for  the  divergences  we  now  find.  (See  Origin  of 
Species,  6th  ed.,  p.  355.) 

It  seems  to  me  that  the  divergences  presented  by  the  varieties  and 
species  of  the  family  Achatinellidae  are  at  variance  with  this  assump- 
tion. Not  only  are  islands  in  sight  of  each  other  occupied  by  diver- 
gent species,  but  different  parts  of  the  same  mountain  range  exposed 
to  the  same  winds  and  rains  and  clothed  with  the  same  vegetation  are 
the  homes  of  divergent  forms. 

Turning  to  the  map  of  the  island  of  Oahu,  we  find  a  mountain  range 
extending  36  miles  from  northwest  to  southeast,  nearly  parallel  with 
the  northeast  coast.  The  northeast  side  of  this  range  is  exposed  to 
the  trade-winds  fresh  from  the  ocean,  and  accordingly  receives  a 
heavier  rainfall  than  the  other  side ;  but  there  is  not  much  difference 
in  the  amount  of  rain  received  by  the  different  valleys  on  one  side  of 
the  mountain.  In  nearly  all  these  valleys  on  either  side  of  the  range 
are  found  shady  groves  of  what  the  natives  call  the  "kukui"  (Aleu- 
rites  triloba).  Many  species  of  the  genera  Achatinella  and  Bulimella 
have  their  haunts  in  these  groves,  some  species  clinging  to  the  leaves 
and  young  branches,  and  others  to  the  trunks  and  the  larger  branches. 
Most  of  the  species  thrive  only  where  the  shade  is  dense  and  the  atmos- 
phere laden  with  dampness  a  large  portion  of  each  month. 

The  student  who  starts  with  the  assumption  that  divergent  varie- 
ties and  species  arise  only  through  exposure  to  different  environments 
will  expect  that  these  groves,  at  least  those  on  the  same  side  of  the 
mountain  range,  will  be  occupied  by  the  same  species.  Having  found 
one  set  of  species  in  a  given  valley,  when  he  comes  to  a  valley  ten 
miles  distant,  possessing  the  same  conditions  of  soil,  rainfall,  vegeta- 
tion, and  shade,  where  the  birds,  reptiles,  and  insects  are  the  same, 
where  the  mice  and  ants,  their  only  known  enemies,*  are  the  same,  he 
naturally  looks  on  the  leaves  and  branches  of  the  familiar  trees  for 


*  The  species  that  molest  the  snails  were  not  known  on  these  islands  till  com- 
paratively recent  times. 


DIVERGENCE   NOT   ALWAYS   ADVANTAGEOUS.  217 

the  snails  he  has  found  in  similar  stations  not  far  distant ;  but  what  is 
his  surprise  to  find  only  different  species,  all  allied  to,  but  quite  dis- 
tinct from,  those  he  has  previously  known !  Twenty  miles  from  the 
first  valley  he  renews  his  investigations,  finding  the  forms  of  all  the 
different  groups  still  more  divergent,  though  all  the  conditions  of  the 
environment  are,  so  far  as  he  can  observe,  the  same. 

He  finally  perceives  that  he  must  give  up  the  theory  that  the  cause 
of  this  divergence  is  exposure  to  different  environments. 

(3)  When  the  environment  is  the  same  in  two  districts  occupied  by 
allied  species  or  varieties,  it  is  evident  that  the  differences  that  distinguish 
the  latter  can  not  be  advantageous,  even  though  their  differences  include 
strongly  contrasted  habits.  For  in  order  that  these  differences  should 
be  advantageous,  it  is  necessary  not  only  that  they  should  relate  to 
the  performance  of  vital  functions,  and,  therefore,  be  differences  of 
adaptation,  but  it  is  necessary  that  these  differences  of  adaptation 
should  relate  to  differences  in  the  environment,  so  that  the  forms 
would  be  at  some  disadvantage  if  they  should  exchange  districts. 
Advantageous  differences  are  always  adaptational ;  but  adaptational 
differences  are  not  always  advantageous,  and  in  such  cases  the  diver- 
gence can  not  be  primarily  attributed  to  diversity  in  the  action  of 
natural  selection  in  the  different  districts.  Under  the  protection  of 
isolation,  diversity  of  selection  may  arise  which  helps  in  producing 
divergence ;  but  when  the  environments  are  the  same,  the  divergence 
is  in  no  sense  advantageous ;  for,  if  a  given  combination  of  characters 
is  an  advantage  in  one  district,  so  would  it  also  be  in  the  other  dis- 
trict, and  the  difference  or  divergence  is  no  advantage. 

A  familiar  example  will  perhaps  put  the  distinction  between  the 
causes  of  survival  and  transformation  and  the  causes  of  divergent  sur- 
vival and  transformation  in  a  clearer  light.  The  forms  of  language 
are  growths  that  are  governed  by  the  laws  of  utility  as  fully  as  the 
forms  of  varieties  and  species.  Each  language  and  each  part  of  a 
language  exists  and  persists  only  as  it  is  found  to  be  of  use.  The  ' '  sur- 
vival of  the  fittest"  is  a  law  that  is  perhaps  as  conspicuous  in  the 
domain  of  language  as  in  the  organic  world.  Again,  every  language, 
like  every  organic  species,  is  in  many  respects  determined  by  the 
environment.  A  language,  for  example,  developed  in  Java  will  pre- 
sent names  for  many  plants  and  animals  that  will  not  be  represented 
in  a  language  developed  in  Greenland.  But,  granting  all  this,  does  it 
follow  that  linguistic  differences  are  necessarily  advantageous?  The 
Polynesian  system  of  counting  by  fours,  and  the  Eskimo  system  that 
proceeds  by  scores,  are  undoubtedly  useful  systems;  but  is  there  any- 
thing advantageous  in  the  difference?     I  think  hot,  for  each  system  is 


2l8  APPENDIX   II — INTENSIVE   SEGREGATION. 

as  well  adapted  to  the  environment  of  the  other  as  to  its  own  envi- 
ronment. We  may  look  upon  the  more  important  parts  of  a  language 
as  persisting  through  their  usefulness,  the  survival  of  the  fittest  being 
the  law;  but  the  divergent  evolution  which  brings  several  languages 
out  of  one  seems  to  be  principally  due  to  other  principles  which  are 
closely  akin  to  the  principles  that  produce  divergence  in  the  organic 
world.  The  fundamental  condition  in  both  organic  and  linguistic  diver- 
gence is  isolation;  and,  this  being  secured,  diversity  of  habits,  bring- 
ing diversity  of  aptitudes  and  diversity  in  the  forms  of  survival,  is  sure  to 
arise  even  when  the  environment  is  the  same. 

(4)  Specific  differences  are  not  always  differences  of  adaptation  to  the 
environment,  and  those  that  are  not  should  not  be  attributed  to  the  action 
of  natural  selection.  It  is  admitted  by  every  one  that  a  distinction 
relating  to  a  character  that  is  of  no  use  in  the  economy  of  the  organism 
can  not  have  arisen  under  the  influence  of  natural  selection.  Those 
who  maintain  that  all  specific  distinctions  are  due  to  natural  selection 
maintain  at  the  same  time  that  these  distinctions  are  adaptational 
and  advantageous.  There  are  naturalists  who  maintain  that  the 
very  essence  of  the  Darwinian  theory  is  ' '  that  specific  differences  must 
be  advantageous,"*  and,  therefore,  adaptational,  while  they  do  not 
claim  the  same  for  generic,  family,  and  ordinate  distinctions,  or,  indeed, 
for  varietal  distinctions,  if  I  rightly  understand.  I  have  never  seen 
any  attempt  to  explain  this  supposed  exception  in  the  midst  of  the 
taxonomic  series ;  and  it  seems  to  me  that  the  break  in  the  continuity 
of  nature  which  this  interpretation  of  the  Darwinian  theory  supposes 
should  lead  us  to  a  very  careful  investigation  of  the  facts  before  we 
accept  it  as  a  true  interpretation  of  nature. 

I  shall  content  myself  with  pointing  out  one  distinction,  occasion- 
ally occurring  between  allied  species,  for  which  no  use  has  ever  been, 
or  is  likely  to  be,  found.  I  refer  to  the  distinction  between  what  are 
known  as  dextral  and  sinistral  forms.  This  distinction  relates  to  the 
form  of  the  twisting  of  the  animal  and  its  shell.  It  is  most  easily 
recognized  by  holding  the  shell  with  the  aperture  toward  you  with 
the  apex  turned  upward,  and  observing  whether  the  aperture  lies  on 
the  right  side  of  the  central  columella  of  the  shell  or  on  the  left. 
In  the  first  case  it  is  described  as  dextral,  in  the  second  as  sinistral. 
In  most  families  and  genera  of  water  mollusks  the  sinistral  form  occurs 
only  as  a  sport  (as  in  man  the  heart  is  sometimes  found  on  the  right 
side),  and  even  among  air-breathing  mollusks  the  dextral  form  vastly 
predominates.      Of  the  Achatinellidae,  Amastra  and  Leptachatina, 


*  See  letter  from  Mr.  W.  T.  Thiselton  Dyer,  in  Nature,  vol.  xxxix,  p.  8 


NATURAL  SELECTION   NOT  ALWAYS  THE  CAUSE.  219 

which  are  genera  of  terrestrial  habits,  are  (with  but  few  exceptions) 
dextral  in  form ;  while  the  other  genera,  which  are  plant  feeders  and 
constantly  hanging  to  branches  or  leaves,  present  many  species  that  are 
constantly  sinistral,  and  many  others  that  are  both  dextral  and  sinis- 
tral. Why  should  Achatinella  adusta  in  Pauoa  and  Makiki  be  constantly 
sinistral  when  the  most  nearly  allied  A.  producta  found  in  the  same 
valleys  is  both  dextral  and  sinistral  ?  Why  should  A .  bacca  and  A . 
ahbreviata  in  Palolo  and  Waialae  be  constantly  dextral  when  other 
species  of  Achatinella  in  the  same  valleys  are  for  the  most  part  sinistral  ? 
Is  there  any  adaptation  to  the  environment  possessed  by  a  dextral 
form  which  would  be  lost  if  the  form  was  reversed?  If  not,  natural 
selection  could  not  have  anything  to  do  with  that  part  of  its  char- 
acter. Bulimella  rosea  is  s\n\stra.\,vihi\e:  B.  bulimoides  is  deyittaX.  If 
in  this  respect  they  should  exchange  forms,  would  any  disadvantage 
be  experienced  by  either  species?  It  is  impossible  to  conceive  of  any 
disadvantage  that  would  follow,  and,  therefore,  I  can  not  believe  that 
this  difference  in  the  two  species  was  in  the  first  place  due  to  natural, 
sexual,  or  any  other  form  of  selection. 

There  are  many  other  specific  distinctions  presented  in  this  family 
which  seem  to  be  of  no  advantage,  though  they  are  not  so  far  removed 
from  all  suggestion  of  the  possibility  of  use  as  the  character  we  have 
just  been  considering.  The  brilliant  colors  and  varied  patterns  pre- 
sented by  many  of  the  arboreal  species  would  be  of  advantage  to  them- 
selves if  they  served  as  warning  of  nauseous  qualities  to  creatures  that 
are  liable  to  prey  upon  them ;  but  no  such  conditions  exist.  The  birds 
of  the  forest  region  are  for  the  most  part  fruit  and  nectar  feeding ; 
and  the  ants  and  mice  which  in  recent  years  have  made  sad  havoc 
with  the  mountain  snails  unfortunately  do  not  spare  the  highly  colored 
species. 

There  can  be  no  doubt  that  when  representatives  of  different  genera 
occupy  the  same  trees  they  remain  segregated  through  the  influence 
of  sexual  instincts,  which  must  be  associated  with  some  means  of  rec- 
ognizing those  of  their  own  group ;  but  it  is  not  at  all  probable  that 
the  colors  and  patterns  of  any  species  are  recognized  by  their  mates, 
or  have  been  developed  under  the  influence  of  sexual  selection. 
There  is,  therefore,  strong  reason  to  doubt  whether  selection  of  any 
kind  has  been  concerned  in  the  production  of  the  beautiful  colors  and 
patterns  of  these  species,  unless  possibly  correspondences  in  color 
within  the  limits  of  a  genus  are,  in  some  cases,  due  to  the  inheritance 
of  tendencies  produced  by  selection  when  conditions  were  very  differ- 
ent from  what  we  now  find.  But  the  divergences  in  color  and  pattern 
in  the  species  of  one  genus  can  not  be  thus  explained. 


220  APPENDIX   II — INTENSIVE    SEGREGATION. 

(5)  The  average  radius  of  distribution  for  species  of  the  same  value  in 
allied  genera  varies  in  the  different  genera  directly  as  the  average  power 
and  opportunity  for  migrating,  and  inversely  as  the  plasticity  and  vari- 
ability of  each  genus.  Comparing  the  distribution  of  the  HeHces  of 
Europe  with  that  of  the  Achatinellidae  of  Oahu,  the  most  striking  con- 
trast is  found  in  the  size  of  the  areas  occupied  by  the  different  species. 
Helix  pomatia  is  distributed  from  England  to  Turkey,  over  an  area 
2,000  miles  in  length,  while  of  the  eight  genera  of  Achatinellidae  on 
Oahu  I  know  of  but  one  species  that  seems  to  be  distributed  over 
the  whole  36  miles  of  the  main  mountain  range,  and  this  one  is  rep- 
resented by  three  varieties  belonging  to  different  parts  of  the  range 
and  perhaps  worthy  to  be  regarded  as  different  species.  The  species 
to  which  I  refer  is  Auriculella  auricula  (Per.),  the  typical  forms  of  which 
are  found  on  the  eastern  half  of  the  mountain  range.  On  the  other 
half  of  the  range  we  find  the  closely  allied  forms  to  which  I  have  given 
the  manuscript  names  solida  and  pellttcida.  This  great  contrast  in  the 
size  of  the  areas  occupied  must  be  due  either  to  the  greater  plasticity 
of  the  Achatinellidae  or  to  their  having  inferior  opportunities  for 
migrating,  or  to  both  causes.  As  I  become  better  acquainted  with 
the  great  difference  in  the  habits  and  circumstances  of  the  contrasted 
species,  I  give  increasing  weight  to  the  difference  in  the  opportunities 
for  migrating.  With  the  continental  species,  floods  must  be  one  great 
means  of  distribution ;  but  in  the  case  of  the  insular  species,  the  floods 
would  carry  floating  individuals  upon  the  grassland  or  into  the  sea, 
in  either  case  to  perish.  Again,  the  habit  of  traveling  upon  the  ground, 
which  belongs  to  most  of  the  Helices  of  Europe  and  America,  gives 
incalculable  opportunities  for  migration  which  are  not  enjoyed  by 
species  that  are  strictly  arboreal,  as  are  many  of  the  Hawaiian  species. 
Most  of  the  Hawaiian  snails  are  still  further  restricted  in  their  oppor- 
tunities by  their  inability  to  resist  a  dry  atmosphere  or  exposure  to  the 
sun,  which  renders  it  necessary  that  they  should  remain  in  the  isolated 
areas  that  are  favored  with  shade  in  the  different  valleys. 

The  habits  of  the  different  genera  occupying  Oahu  are  also  instruc- 
tive as  throwing  light  upon  the  relative  areas  occupied  by  the  species 
of  the  different  genera.  Achatinella  and  Bulimella  seem  to  be  the 
most  restricted  in  their  opportunities  for  migrating ;  first,  because  they 
are  entirely  arboreal  in  their  habits,  clinging  to  the  trunks  and  branches 
of  trees  through  their  whole  life  history;  and,  second,  because,  for 
the  most  part,  they  occupy  the  shady  and  damp  thickets  and  groves, 
the  shade  in  each  valley  being  separated  from  similar  shades  in  adjoin- 
ing valleys  by  lofty  and  sparsely  wooded  mountain  ridges  at  each  side 
of  the  valley  and  by  open  grassland  at  the  mouth  of  the  valley.     On 


AVERAGE   RADIUS   OF   DISTRIBUTION.  221 

the  Other  hand,  Apex,  which  for  the  most  part  occupies  trees  and 
shrubs  on  the  ridges  which  are  connected  with  each  other  through  the 
central  ridge  of  the  mountain  range,  and  Amastra  and  Leptachatina, 
which  are  for  the  most  part  found  on  the  ground  under  dead  and  de- 
caying leaves,  seem  to  possess  better  opportunities  for  migration  than 
either  the  Achatinella  or  Bulimella.  Corresponding  with  these  facts 
we  find  the  species  of  Achatinella  and  Bulimella  especially  limited  in 
the  areas  they  occupy,  while  the  species  of  Apex,  Amastra,  and  Lep- 
tachatina  are  less  so.  For  example,  the  area  occupied  by  Amastra 
turritella,  A.  tristis,  and  A.  ventulus  includes  the  areas  occupied  by 
many  species  of  Achatinella  and  Bulimella;  and  Apex  loratus  and 
A .  pallidus,  occupying  the  mountain  ridges,  range  from  Makiki  to 
Halawa,  exceeding  the  range  attained  by  any  arboreal  species  occupy- 
ing the  valleys  of  the  same  region. 

(6)  When  a  group  of  divergent  forms  that  are  fertile  with  each  other  is 
being  developed  through  the  influence  of  local  or  geographical  isolation, 
other  conditions  remaining  constant,  the  number  of  forms  that  will  be  pro- 
duced within  a  given  area  will  vary  inversely  as  the  square  of  the  average 
radius  of  distribution  for  the  different  forms.  As  this  average  radius  of 
distribution  may  be  taken  as  the  measure  of  the  power  and  opportu- 
nities for  migration,  we  may  say  that,  other  powers  and  opportunities 
remaining  constant,  the  number  of  species  developed  within  a  given  area 
will  vary  inversely  as  the  square  of  the  average  power  and  opportunities  for 
migration. 

Though  migration  is  in  one  sense  a  cause  of  isolation,  it  is  evident 
that  the  number  of  isolated  groups  of  individuals  of  a  given  form 
within  a  given  area  does  not  increase  with  the  increase  of  migration. 
Isolation  is  produced  by  the  great  contrast  between  ordinary  and  extraor- 
dinary combinations  of  opportunities  for  migration;  and  this  contrast  is 
liable  to  be  as  great  in  the  case  of  species  that  have  limited  powers 
and  opportunities  as  in  the  case  of  those  that  have  very  great  powers 
and  opportunities.  The  number  of  isolations  thus  produced  that  can 
exist  within  the  limits  of  a  given  area  must  vary  inversely  as  the  square 
of  the  power  and  opportunity  for  migration. 

The  facts  of  distribution  we  have  been  considering  seem  to  corre- 
spond to  this  law. 

(7)  Forms  that  are  most  nearly  related,  and  are,  therefore,  the  least 
subject  to  sexual  and  impregnational  isolation,  are  distributed  in  such  a 
manner  that  their  divergence  is  directly  porportional  to  their  distance 
from  each  other,  which  is  also  the  measure  of  the  time  and  degree  of  their 
geographical  isolation;  while  those  most  manifestly  held  apart  by  sexual 
instincts  and  impregnational  incompatibilities  do  not  follow  this  law. 


222  APPENDIX    II — INTENSIVE    SEGREGATION. 

Bulimella  is  represented  by  two  groups  of  species,  one  of  ovate  form, 
the  other  elongated  and  with  the  outlines  of  the  spire  less  rounded. 
The  widest  divergence  between  these  groups  is  presented  by  species 
occupying  the  same  districts  and  valleys,  but  the  widest  divergences  in 
the  species  of  either  of  these  groups  are  found  in  valleys  widely  sepa- 
rated. In  the  latter  case,  the  degree  of  geographical  separation  is  prob- 
ably an  approximate  measure  of  the  time  and  degree  of  isolation,  and, 
therefore,  the  measure  of  the  degree  of  divergence ;  while,  in  the  former 
case,  the  isolation  is  probably  as  complete  between  forms  occupying 
the  same  valley  as  between  those  of  widely  separated  valleys.  There  is 
reason  to  believe  that  in  the  eastern  part  of  the  island  these  two  groups 
are  not  fully  held  apart  by  sexual  isolation  or  segregate  fecundity 
and  vigor,  for  there  is  complete  intergrading,  and  the  divergence 
between  the  groups  in  any  one  valley  is  much  less  than  is  found  in  the 
northwest  portion  of  the  island,  where  sexual  incompatibility  seems 
to  be  complete. 

Achatinella  bacca  andyl.  abhreviata  completely  intergrade  with  each 
other,  but  they  are  associated  with  a  number  of  other  species  of  Acha- 
tinella with  which  they  do  not  intergrade,  prevented,  it  seems  to  me,  by 
mutual  incompatibility.  We  have,  therefore,  in  the  eastern  valleys 
two  groups  of  Achatinella  completely  segregated  from  each  other, 
though  occupying  the  same  districts  and  in  some  measure  the  same 
stations;  while  in  the  other  valleys  the  two  groups  coalesce,  the 
different  species  occupying  any  one  valley  being  only  partially  isolated 
by  divergent  habits  of  feeding. 

The  dififerent  genera  and  subgenera,  which  are  undoubtedly  segre- 
gated by  divergent  sexual  instincts,  as  well  as  by  physiological  incom- 
patibilities, are  equally  divergent,  whether  we  compare  forms  from 
the  same  or  from  distant  valleys. 

(8)  The  distribution  of  the  varieties,  species,  and  genera  of  Achati- 
nella on  this  island  is  just  such  as  would  be  produced  by  divergent  evolu- 
tion which  depends  on  isolation  as  a  necessary  condition,  even  when  the 
environments  are  different,  and  which  always  follows  long-continued 
isolation,  even  when  the  environment  surrounding  the  different  sections 
is  the  same. 

It  may  be  safely  said  of  the  multitude  of  varieties  which  inhabit  the 
island  of  Oahu  that  every  one  is  more  or  less  segregated  from  all  other 
varieties ;  and  I  believe  this  will  be  found  true  concerning  varieties 
in  every  part  of  the  world.  This  fundamental  fact  would  probably 
never  have  been  denied,  except  for  the  delusive  idea  that  the  advan- 
tage of  divergence  would  lead  to  the  accumulation  of  divergence 
even  if  segregation  were  entirely  wanting.     What  could  be  a  greater 


DIVERGENCE   DEPENDS   ON   ISOLATION.  223 

mistake  for  the  breeder  of  animals  than  to  imagine  that  by  selecting 
extreme  variations  and  breeding  them  together  he  would  in  time 
secure  well-marked  races?  It  must  be  equally  at  variance  with  fact 
to  suppose  that  any  advantage  secured  by  divergent  variations  can 
be  preserved  and  accumulated  while  the  different  forms  are  freely 
intergenerating. 

In  the  family  we  are  considering,  the  chief  forms  of  isolation  are 
probably  what  I  have  called  local,  geographical,  industrial,  and  sexual 
isolation,  strengthened  in  many  cases  by  segregate  fecundity  and  vigor. 
As  illustrating  local  isolation  I  would  mention  varieties  and  species 
of  Apex,  for  the  most  part  occupying  mountain  ridges  which  are  all 
connected  with  each  other,  without  the  intervention  of  geographical 
barriers.  Geographical  isolation  is  illustrated  in  the  forms  of  Achati- 
nella  and  Bulimella,  which  for  the  most  part  occupy  the  deep  valleys, 
the  ridges  forming  barriers  that  are  very  rarely  surmounted.  Indus- 
trial isolation  is  illustrated  by  the  closely  allied  varieties  of  one  group 
of  species  that  occupy  one  valley,  but  are  prevented  from  crossing  by 
different  habits  of  feeding.  It  is  probable  that  sexual  or  seasonal  iso- 
lation prevents  the  pairing  of  Achatinella  with  Bulimella  when  both 
occupy  the  same  trees.  Moreover,  cross  sterility  would  undoubtedly 
prevent  the  multiplication  of  the  hybrids,  if  cross-unions  ever  do  occur 
between  forms  so  widely  divergent.  There  can  be  no  doubt  that  the 
same  principles  prevent  the  strongly  marked  groups  of  either  genus 
from  intergenerating;  as,  for  example,  in  the  case  of  Achatinella  bacca 
and  A.  abbreviata,  which  are  intergraded  with  each  other,  but  not 
with  the  surrounding  species  of  Achatinella. 

Again,  divergent  forms  of  environal  selection  do  not  necessarily 
depend  on  exposure  to  different  environments.  Industrial  isolation 
is  produced  by  different  modes  of  using  the  environment  found  in  a 
single  district ;  and  the  same  cause  will  often  produce  diversity  in  the 
forms  of  environal  selection  affecting  the  isolated  sections,  distrib- 
uted in  different  districts,  but  exposed  to  the  same  environment. 
Cumulative  divergence  in  the  methods  of  using  the  environment  in 
the  different  sections  of  the  species  depends  upon  their  isolation, 
and,  therefore,  increasing  divergence  in  the  forms  of  selection  affect- 
ing the  different  branches  depends  upon  their  isolation.  Geograph- 
ical isolation  under  the  same  environment,  if  it  does  not  of  itself 
produce  divergent  forms  of  selection,  opens  the  way  for  change  in  the 
habits  of  feeding,  with  diversity  of  selection  in  the  different  sections  of 
the  species.  Take,  for  example,  the  species  of  Achatinella :  In  Manoa 
and  Makiki  they  chiefly  occupy  the  kukui  {A  leurites  triloba)  and  other 
trees,  while  in  Kawailoa  and  that  region  they  neglect  the  larger  trees 
and  take  to  the  lobelia  and  other  shrubs  and  herbaceous  plants. 


224  APPENDIX  II — INTENSIVE   SEGREGATION. 

But  why  should  the  degree  of  divergence  increase  with  the  contin- 
uance of  the  isolation?  The  answer  seems  to  be  that  the  combined 
effects  of  the  different  principles  of  transformation  in  the  isolated 
groups  increase  with  the  time  of  isolation;  and,  as  independent 
transformation  is  never  parallel,  the  divergence  increases  in  the  same 
ratio.  Diversity  of  environal  selection  is  undoubtedly  one  of  the  prin- 
ciples producing  this  divergence,  even  when  the  vegetation  and 
physical  conditions  of  the  different  districts  are  the  same,  for  when  the 
habits  of  feeding  change,  the  environal  selection  must  usually  change. 
But  there  are  cases  of  divergence  accompanying  isolation  in  which 
the  habits  of  feeding  seem  to  have  remained  unchanged ;  and  in  such 
cases  I  explain  the  divergence  by  the  fact  that  any  small  fragment  of 
a  species  is  incapable  of  propagating  all  the  qualities  of  the  species  in 
the  exact  proportion  presented  by  the  average  of  the  species. 

2.  Similar  Facts  in  Other  Regions. 

Many  of  the  facts  embodied  in  these  eight  propositions  must  have 
been  observed  wherever  naturalists  have  studied  the  geographical  dis- 
tribution of  the  varieties  and  species  of  polymorphic  genera ;  but  in  the 
distribution  of  the  Achatinellidae  there  are  features  of  peculiar  interest 
arising  from  the  fact  that  the  powers  of  migration  possessed  by  the 
species  of  the  surrounding  environment  are  very  much  greater  than 
those  possessed  by  these  molluscan  species.  Through  this  circum- 
stance a  comparatively  uniform  environment  is  produced  in  which  the 
effects  of  independent  generation  unmodified  by  the  effects  of  changed 
environment  may  be  observed.  The  remarkable  facts  of  distribution 
which  we  have  on  the  island  of  Oahu  are  found  in  other  parts  of  the 
Hawaiian  Islands,  wherever  this  family  occurs.  I  am  also  fully  con- 
vinced that,  in  other  parts  of  the  world,  wherever  one  genus  or  family 
of  very  low  powers  of  migration  is  surrounded  by  a  body  of  plant  and 
animal  forms  possessing  much  higher  powers  of  migration,  there  similar 
facts  will  present  themselves  whenever  investigation  is  made. 

The  distribution  of  land  mollusks  belonging  to  the  genus  Partula 
found  on  the  Society  Islands  present  similar  features.  The  island  of 
Reiatea,  which  is  but  14  miles  in  length  and  3  or  4  miles  in  breadth,  is 
the  home  of  about  30  species  and  varieties,  most  of  which  are  confined 
to  areas  only  a  few  square  miles  in  extent.  I  am  not  informed  as  to 
the  distribution  of  the  plants  on  which  these  species  feed,  but  there  is 
no  reason  to  suppose  they  occupy  limited  districts  corresponding  to 
those  occupied  by  the  different  species  of  Partula.* 


*  See  Bulletin  of  the  Museum  of  Comparative  Zoology  at  Harvard  University, 
vol.  I.X,  No.  5. 


DIVERGENCE  IN  INSECTS.  225 

III.  Divergence  in  Insects. 

The  dependence  of  divergence  on  some  form  of  isolation  is  most 
clearly  exemplified  in  insects,  and  though  my  studies  are  but  limited  in 
that  field,  I  shall  refer  to  a  few  cases,  which  may  serve  to  direct  atten- 
tion to  a  class  of  facts  of  the  highest  interest  not  only  to  entomology, 
but  to  general  biology. 

1.  Divergence  in  Erynnis  and  Thanaos. 

Erynnis  {Pamphila)  and  Thanaos  {Nisoniades) . — These  two  genera 
of  small  North  American  butterflies  are  worthy  of  the  special  atten- 
tion of  those  who  are  studying  the  problems  of  divergent  evolution,  for 
they  furnish  strong  indications  that  organisms  which  are  with  diffi- 
culty distinguished  from  each  other  by  external  form  or  color  may,  nev- 
ertheless, be  well-established  species  segregated  presumably  by  sexual 
instincts  corresponding  to  sexual  characters  by  which  those  of  opposite 
sexes  of  the  same  species  readily  recognize  each  other,  and  probably 
cut  ofiF  from  the  possibility  of  producing  hybrids  through  incompati- 
bility of  physiological  endowments.  In  the  origin  of  some  of  these 
species  geographical  isolation  may  have  had  an  important  influence; 
but  concerning  others  there  can  hardly  be  a  doubt  that  the  segregative 
influences,  holding  apart  species  that  occupy  the  same  districts,  were, 
from  an  early  stage,  peculiarities  of  their  sexual  instincts  and  constitu- 
tion. The  reason  for  accepting  this  view  of  their  origin  is  found  in  the 
fact  that,  though  slightly  divergent  in  other  points,  the  characters  by 
which  they  are  clearly  distinguished  are  found  in  the  forms  of  the  male 
genitalia ;  and  in  the  characters  of  these  organs  we  find  clearly  marked 
species,  for  the  most  part  free  from  the  intergrading  forms  which  would 
certainly  be  presented  if  the  dififerent  species  were  not  prevented  from 
crossing  by  sexual  instincts  or  constitution. 

A  full  description  of  these  genera,  with  observations  on  the  asymmet- 
rical development  of  the  right  and  left  sides  of  the  genital  armature 
in  Thanaos,  will  be  found  in  Scudder's  Butterflies  of  New  England. 
(See  also  Mem.  Boston  Soc.  Nat.  Hist.,  ii  (1874),  and  Proceedings  of  the 
same  Society  for  April  27,  1870,  vol.  xiii  (1871),  p.  282. 

2.  Divergence  in  Basilarchia. 

(i)  Basilarchia  (Scudder)  is  an  attractive  genus  of  butterflies  pecu- 
liar to  North  America,  where  it  is  represented  by  four  or  five  species. 
Three  of  these  are  found  in  New  England,  and  are  minutely  described 
in  Scudder's  "Butterflies  of  New  England,"  from  which  I  draw  my 
information  (pp.  250-305). 


226  APPENDIX  II— INT^NSIVS   SEGREGATION. 

r 

The  distribution  of  these  three  species  is  of  great  interest,  as  it  illus- 
trates divergence  both  with  and  without  local  segregation.  Basil- 
archia  archippus  ranges  over  nearly  the  whole  United  States  and  over 
the  southern  portion  of  Canada.  B.  astyanax  occupies  the  valley  of 
the  Mississippi  and  eastward  to  the  Atlantic  from  the  Gulf  of  Mexico 
on  the  south  to  the  lakes  on  the  north.  B.  arthemis  is  distributed  from 
Newfoundland  and  Nova  Scotia  on  the  east,  over  New  England,  Can- 
ada, the  region  of  the  lakes,  away  to  the  northwest,  toward  the  con- 
fines of  Alaska.  It  will  be  observed  that  the  area  of  distribution  of  B. 
archippus  includes  the  whole  of  that  of  B.  astyanax  and  a  large  portion 
of  that  of  B.  arthemis;  while  the  areas  of  B.  astyanax  and  B.  arthemis 
overlap  along  the  whole  northern  border  of  the  territory  occupied  by 
B.  astyanax.  This  area  of  overlapping  distribution  in  which  the  three 
species  are  associated  is  about  i,ooo  miles  in  length  and  from  loo  to 
250  miles  in  width. 

(2)  Forms  of  Isolation  that  separate  Basilarchia  archippus  from  B. 
astyanax  and  B.  arthemis. — It  is  evident  that,  in  the  present  condition 
of  distribution,  geographical  barriers  and  territorial  separation  have 
nothing  to  do  with  the  integrity  of  B.  archippus  as  a  separate  species. 
In  other  words,  it  is  not  under  the  influence  of  geographical  or  local 
isolation.  Whatever  may  have  been  its  past  history,  these  certainly 
are  not  the  causes  that  at  present  prevent  it  from  interfusing  with 
other  species  of  Basilarchia  with  which  it  is  associated. 

Again,  seasonal  isolation  seems  to  have  but  little  influence;  for 
thought,  archippus  seems  to  appear  15  or  20  days  earlier  than  the 
other  species,  the  remainder  of  the  breeding  season,  which  extends 
over  many  weeks,  is  coincident. 

The  habits  and  feeding  instincts  of  this  species  must  tend  to  sepa- 
rate it  somewhat  from  B.  arthemis,  for  this  latter  species  frequents 
forest  regions,  especially  when  elevated  and  hilly,  while  B.  archippus 
is  found  in  the  open  country  in  fields  and  meadows,  especially  in  low 
levels.  The  eggs  of  B.  arthemis  are  chiefly  deposited  on  the  species  of 
birch  and  willow  that  are  found  on  the  highlands;  while  the  eggs  of  B. 
archippus  are  chiefly  deposited  on  the  willows  and  poplars  found  on 
the  lowlands,  though  on  the  White  Mountains  it  occasionally  extends 
its  range  to  as  high  levels  as  B.  arthemis.  There  is,  therefore,  between 
these  species  a  slight  degree  of  industrial  isolation ;  but  this  partial 
segregation  does  not  prevent  their  being  often  found  in  the  same 
fields,  and  unless  held  apart  by  sexual  instincts  and  by  partial  infer- 
tility, hybrids,  which  are  now  very  rare,  would  be  very  common. 

We  are,  therefore,  led  to  believe  that  diversity  of  sexual  instincts, 
accompanied  by  a  considerable  degree  of  cross-sterility,  is  the  chief 


PARTIAL  ISOLATION  ILLUSTRATED.  227 

cause  preserving  the  independent  character  of  this  species.  Except 
for  the  sexual  segregation  and  segregate  fecundity  there  is  every  rea- 
son to  beHeve  that  this  species  could  never  have  arisen,  or,  if  it  had 
arisen  as  a  variety  in  some  isolated  locality ,  would  have  been  submerged 
in  the  allied  forms  when  its  wider  distribution  was  reached.  This  con- 
clusion, which  has  been  reached  by  observing  the  general  relations  of 
the  species,  is  confirmed  by  a  minute  examination  of  the  structure  of 
the  three  species.  We  find  that  while  the  male  genitalia  of  B.  astyanax 
and  B.  arthemis  differ  but  slightly,  those  of  B.  archippus  are  consider- 
ably divergent.  This  is  an  index  of  the  psychological  and  physiolog- 
ical relations  of  varieties  and  species  of  no  small  importance ;  for  a 
comparison  of  many  species  shows  that  differences  of  this  kind  are 
usually  accompanied  by  corresponding  degrees  of  segregation  in  sexual 
instincts  and  of  cross-sterility.  In  other  words,  we  find  that  difference 
in  the  male  genitalia,  which  is  a  form  of  structural  segregation,  is  an 
index  of  sexual  segregation  and  segregate  fecundity. 

(3)  The  Partial  Isolation  of  B.  astyanax  and  B.  arthemis. — In  the 
relation  of  these  two  species  we  find  examples  of  segregative  influences 
differing  somewhat  from  those  that  have  just  been  found  in  the  case  of 
B.  archippus.  Regional  isolation,  with  exposure  to  different  climates 
and  adaptations  to  different  food-plants,  has  undoubtedly  had  an 
important  influence  in  the  formation  of  these  species ;  but,  in  the  part 
of  the  country  where  they  coexist,  their  life-histories  correspond  com- 
pletely, and  cross-unions  seem  to  be  frequent.  The  hybrid  form  has 
been  described  as  a  separate  species,  and  some  entomologists  have 
classed  it  as  a  dimorphic  form  of  B.  arthemis;  but  Scudder  gives  several 
reasons  for  believing  that  it  is  the  result  of  cross-unions  between  these 
two  species.  There  are,  however,  several  reasons  for  believing  that 
partial  segregate  fecundity  exists  between  the  two  species ;  for,  in  the 
strip  of  territory  where  the  two  are  associated  they  do  not  completely 
coalesce,  as  would  be  the  case  if  they  were  completely  cross-fertile. 
In  Scudder's  Butterflies  of  New  England,  pages  159  and  160,  we  find 
mention  of  two  species  (Cercyonis  alope  and  C .  nephele) ,  in  which  the 
cross-steriUty  must  be  considerably  weaker  than  between  the  two  spe- 
cies we  are  now  considering ;  for,  in  the  intermediate  region  in  which 
their  areas  overlap,  the  intergrade  forms  are  comparatively  abundant. 
Moreover,  the  difference  in  the  male  genitalia  of  B.  astyanax  and  B. 
arthemis,  though  much  less  than  that  which  appears  when  either  of  these 
is  compared  with  B.  archippus,  is  such  as  indicates  a  considerable 
degree  of  infertility. 

In  these  two  species  we  have,  then,  a  good  example  of  partial  isola- 
tion through  distribution  over  areas  which,  though  overlapping,  are 


228  APPENDIX  II — INTENSIVE   SEGREGATION. 

for  the  most  part  distinct,  reinforced  by  partial  segregate  fecundity 
which  mayor  may  not  be  accompanied  by  slightly  divergent  sexual 
instincts.  There  is  also  some  isolation  resulting  from  the  fact  that  the 
plants  on  which  B.  arthemis  seeks  to  deposit  its  eggs  are  chiefly  the 
birches  and  willows  of  the  hilly  country,  while  B.  astyanax  prefers  fruit 
trees  of  the  Rosaceae  family  and  other  plants  that  are  found  in  the 
more  open  country.  These  are,  as  I  have  shown  in  my  paper  on 
"  Divergent  Evolution  through  Cumulative  Segregation,"  exactly  the 
conditions  that  produce,  in  successive  generations,  increasing  degrees 
of  segregate  fecundity. 

(4)  Cumulative  Segregation  in  the  Formation  of  the  above  Species. — I 
judge  that  in  the  relations  to  each  other  of  these  three  species  we  have 
the  results  of  divergent  evolution  through  cumulative  segregation 
very  clearly  illustrated.  In  the  earlier  stages  of  divergence  in  this 
genus,  Basilarchia  archip pus,  with  its  fondness  for  the  open  fields,  must 
have  become  partially  separated  from  the  parent  form  from  which  both 
B.  astyanax  and  B.  arthemis  have  since  sprung.  The  separation  may 
have  been  in  some  measure  due  to  the  methods  of  escaping  from 
enemies;  for  we  find  that  the  form  that  has  kept  to  the  open  country 
has  through  protective  selection  gained  a  very  close  resemblance  to  the 
coloring  of  Anosia  plexippus,  which  is  protected  by  its  disagreeable 
qualities.  The  other  form  has  probably  gained  compensative  advan- 
tages by  keeping  closer  to  the  woodlands.  But  the  partial  segrega- 
tion thus  produced  would  never  have  resulted  in  constant  specific  dif- 
ferences if  segregate  fecundity  had  not  arisen  between  the  two  forms. 
We  may  believe  that  some  form  of  impregnational  segregation  (either 
segregate  structure,  segregate  fecundity,  or  segregate  vigor)  was  early 
introduced,  and  that  under  the  protection  of  this  barrier  the  specific 
distinctions  of  the  two  forms  became  fully  established,  though  even 
now  the  barrier  is  not  so  complete  as  to  entirely  preclude  hybrids 
between  B.  archippus  and  each  of  the  other  species.  Examples  of 
both  these  hybrids  are  described  by  Scudder. 

While  this  segregation  was  being  completed,  one  of  the  two  forms 
thus  created  must  have  become  subject  to  a  new  set  of  segregative  in- 
fluences arising  from  wider  distribution  with  diversity  of  climate  and 
of  habits  of  feeding,  reinforced  by  a  slight  degree  of  segregate  fecun- 
dity. B .  astyanax  ^.nd  B .  arthemis  Sixe  the  two  species  resulting  from 
this  last  segregation,  and  the  process  is  so  far  from  being  complete 
that  wherever  the  areas  of  these  two  species  overlap  a  hybrid  form, 
which  has  been  known  as  B.  proserpina,  appears.  That  it  is  a  hybrid 
is  proved  by  the  fact  that  it ' '  varies  most  toward  astyanax  where  this 
prevails,  and  most  towards  arthemis  where  that  prevails;"  that  it  is 


DIVERGENCE   IN   THE   PERIODICAIv   CICADA.  229 

found  only  in  the  narrow  belt  where  the  two  species  are  brought  into 
contact,  and  that  it  has  been  reported  from  so  many  points  in  this  nar- 
row belt  that  there  is  reason  to  believe  that  it  occurs  wherever  the  two 
species  are  brought  into  contact.  If  our  exposition  of  the  segregations 
to  which  these  species  have  been  subjected  is  correct,  they  are  cumu- 
lative in  two  respects :  first,  because  after  one  segregation  has  been 
established  another  is  superimposed,  and  second,  because  a  partial 
segregation  established  in  one  generation  tends  to  become  more  com- 
plete in  subsequent  generations. 

The  primary  causes  in  the  whole  process  are  the  activities  of  the 
organisms  acting  upon  each  other  and  upon  the  environments  in  such  a 
way  as  to  produce,  in  the  first  place,  independent  generation  with  some 
degree  of  divergence,  and  then  unbalanced  selection  of  different  forms 
producing  transformation,  which,  acting  upon  sections  of  the  species 
that  are  prevented  from  crossing,  result  in  ever-increasing  divergence. 

3.  Divergent  Evolution  in  the  Periodical  Cicada   (Cicada  septendecim)  .* 

In  Cicada  septendecim  we  have  examples  of  two  quite  distinct  diver- 
gences, each  depending  on  its  own  forms  of  segregation,  which  are 
easily  recognized. 

The  life  history  of  this  insect  covers  seventeen  years  and  one  or  two 
months.  The  imago  appears  late  in  May,  and  for  a  little  more  than  a 
month  the  males  make  the  woods  ring  with  their  shrill  stridulations. 
The  eggs,  which  are  deposited  in  the  green  twigs  of  trees,  mature  dur- 
ing the  latter  part  of  July,  and  each  newly  hatched  larva,  dropping  to 
the  ground,  takes  up  a  solitary  subterranean  life,  which  it  follows  till 
its  period  of  seventeen  years  is  nearly  complete.  It  then  appears 
above  the  ground,  passes  into  its  winged  stage,  and  enters  on  a  few 
weeks  of  social  life  which  closes  its  career.  This  species  is  widely  dis- 
tributed in  that  part  of  the  United  States  that  lies  between  the  Atlan- 
tic shores  and  the  Rocky  Mountains,  but  does  not  occur  in  Minne- 
sota, Northern  Michigan,  or  Northern  New  England.  It  is,  however, 
represented  by  two  races  in  every  respect  the  same,  except  that  one 
has  a  life-history  of  thirteen  and  the  other  of  seventeen  years.  The 
thirteen-year  race  prevails  in  the  Gulf  States,  but  in  New  England  and 
the  Middle  States  the  seventeen-year  race  is  alone  found.  In  Illinois, 
Missouri,  Kansas,  and  in  several  of  the  Southern  States  the  two  races 
occur  in  the  same  localities ;  but  it  is  evident  that  even  in  such  localities 
it  is  only  once  in  221  years  that  there  will  be  any  opportunity  for  cross- 
ing between  them,  and  we  are  informed  by  those  who  have  made 


*  My  information  is  chiefly  derived  from  Bulletin  No.  8,  Division  of  Entomology, 
U.  S.  Department  of  Agriculture,  by  Dr.  C.  V.  Riley. 


230  APPENDIX   II — INTENSIVK   SEGREGATION. 

a  special  study  of  the  subject  that  they  do  not  cross  when  these 
opportunities  occur;  for  14,  15,  and  16  year  races  are  not  found. 
These  two  races  are,  therefore,  prevented  from  crossing  by  partial 
local  isolation;  by  cyclical  isolation  rendering  it  impossible  that  a 
brood  of  each  occupying  the  same  locality  should  have  opportunity 
for  crossing  more  than  once  in  seventeen  generations  of  the  shorter- 
lived  race,  or  once  in  thirteen  generations  of  the  longer-lived  race ;  and 
by  sexual  isolation  that  shows  itself  in  diversity  of  instincts  preventing 
them  from  pairing  when  other  conditions  favor. 

Whether  devices  have  been  tried  to  induce  cross-unions,  and  whether 
such  unions  are  unfruitful,  I  have  never  heard ;  but  the  simple  fact 
that  fifteen-year  forms  do  not  appear  in  localities  where  the  two  races 
are  found  indicates  that  in  nature  they  do  not  cross.  Several  such 
localities  have  been  reported,  but  in  none  of  them  has  an  intermediate 
form  been  found.  It  seems,  therefore,  that  we  may  safely  draw  the 
conclusion  that  we  have  here  a  case  of  complete  sexual  segregation  be- 
tween forms  which  to  the  human  eye  are  undistinguishable,  and  which 
call  their  mates  with  stridulations  which  to  the  human  ear  are  the  same. 
Now,  I  claim  that  in  such  races  as  these  we  have  the  beginning  of  diver- 
gent species,  a  beginning  that  lies  in  the  segregative  influences  of  con- 
stitutional and  instinctive  qualities  persistently  inherited  by  the  two 
races,  though  the  naturalist  who  examines  specimens  of  the  two  races 
can  not  distinguish  them.  All  that  is  necessary  to  convert  these  two 
races  into  good  species  is  the  transformation  of  one  or  both  of  them 
while  they  are  thus  prevented  from  crossing;  for  we  may  be  assured 
that  the  results  of  transformation  under  such  circumstances  will  never 
be  completely  parallel. 

Each  of  these  races  is  again  subdivided ;  for  accompanying  each  is 
a  diminutive  form,  differing  somewhat  in  color,  not  so  early  by  eight 
or  ten  days  in  its  first  appearance,  producing  a  quite  distinct  stridula- 
tion,  and  showing  no  disposition  to  associate  with  the  larger  form. 
This  small  form  was  described  in  1851  by  Dr.  Fisher  as  a  new  species 
under  the  name  Cicada  cassinii.  Dr.  Riley,  however,  hesitates  to 
receive  it  as  a  separate  species,  because  the  differences  presented  by 
the  genitalia  are  not  constant.     He  says : 

There  are  sufficient  differences  to  separate  the  two  forms  as  distinct ;  but  while 
the  hooks  of  the  large  kind  (septendecim)  are  quite  constant  in  their  appearances, 
those  of  the  smaller  kind  (cassinii)  are  variable,  and  in  some  few  specimens  are 
indistinguishable  from  those  of  the  large  kind.  This  circumstance,  coupled  with 
the  fact  that  the  small  kind  regularly  occurs  with  both  the  seventeen  and  thir- 
teen year  broods,  would  indicate  it  to  be  a  dimorphic  form  of  the  larger,  and  only 
entitled  to  varietal  rank.* 


*  Bulletin  No.  8,  Division  of  Entomology,  U.  S.  Department  of  Agriculture,  p.  7. 


BROODS   AND   RACES   OF   THE   PERIODICAI^   CICADA.  23 1 

I  consider  this  case  as  of  equal  interest  with  the  previous  one ;  for  it 
is  an  example  of  complete  isolation  between  the  forms  of  one  species 
through  diversity  in  their  instincts.  Whether  these  divergent  in- 
stincts are  sexual  or  social  may  be  a  matter  of  question ;  but  in  either 
case  they  are  effectual  in  preventing  crossing. 

If  future  investigation  shows  that  the  small  form  is  often  produced 
directly  from  the  eggs  of  the  large  form,  it  will  have  but  little  claim  to 
be  regarded  as  a  separate  race ;  but  even  then,  if  the  small  form  breeds 
only  with  its  own  kind,  as  has  been  reported  by  several  observers,  and 
if  the  offspring  persistently  reproduce  the  characters  of  the  parents, 
it  will  have  to  be  considered  something  more  than  a  dimorphic  form 
of  the  large  one.  It  would,  in  this  case,  be  a  dimorphic  form  that  is 
assuming  the  character  of  a  species.  If  the  two  forms  were  without 
segregative  sexual  and  social  instincts,  then,  with  cross-fertility,  the 
small  form  would  be  rapidly  absorbed  by  the  large  form,  which  greatly 
preponderates  in  numbers;  and  with  cross-sterility  the  small  form 
would  rapidly  become  extinct ;  for,  through  the  comparative  scarcity 
of  their  numbers,  the  representatives  of  the  small  form  would  have 
but  little  chance  of  mating  with  each  other. 

On  the  other  hand,  if  the  sexual  and  social  isolation  is  complete, 
it  matters  but  little  whether  the  forms  are  mutually  sterile,  for  the  sep- 
arate races  or  species  will  be  protected  by  the  positive  segregation 
produced  by  the  divergent  instincts,  even  if  the  negative  segregation 
depending  on  structural  incompatibility  and  lack  of  physiological 
adaptation  is  entirely  wanting.  It  is  only  when  associated  with  pos- 
itive segregation  that  is  partial  in  its  results  that  negative  forms  of 
segregation  become  important  factors  in  the  preservation  of  diverging 
forms. 

In  animals  that  pair,  isolation  through  sexual  and  social  instincts 
plays  a  similar  role  in  giving  preemptive  power  to  the  males  of  a  given 
species  over  the  females  of  the  same  species  that  is  played  by  poten- 
tial and  prepotential  isolation  in  organisms  whose  fertilizing  elements 
are  distributed  by  wind  and  water.  In  the  one  case  instinctive 
and  in  the  other  potential  segregation,  arising  between  varieties  of 
the  same  species,  marks  these  varieties  as  being  the  initial  forms 
of  divergent  species. 

This  species  presents  another  form  of  isolation  which  is  of  much  in- 
terest, though  it  has  not  yet  resulted  in  forms  that  can  be  ranked  as 
different  races.  I  refer  to  the  complete  cyclical  segregation  that  exists 
between  dififerent  broods  of  a  given  race  appearing  in  different  years. 
Of  the  thirteen-year  race  there  are  seven  broods  and  of  the  seven- 
teen-year race  fourteen.     As  an  example  of  different  broods  occurring 


232  APPENDIX   II — intensive;    SEGREGATION, 

in  the  same  region  I  would  mention  the  two  broods  in  the  District 
of  Columbia,  one  appearing  in  1885  and  at  intervals  of  seventeen  years 
thereafter,  and  one  appearing  in  1 894  and  at  intervals  of  seventeen 
years  thereafter.  We  have  no  means  of  testing  the  sexual  or  the 
social  instincts  of  these  different  broods,  for  they  never  appear  in  the 
same  year.  No  one  can  say  whether  if  they  could  be  brought  together 
they  would  be  found  as  indisposed  to  breed  with  each  other  as  are  the 
thirteen-year  and  seventeen-year  races.  But,  be  that  as  it  may,  the 
two  forms  are  as  completely  isolated  as  they  can  be,  and  the  oppor- 
tunity for  independent,  and,  therefore,  divergent,  transformation,  is 
much  the  same  as  that  which  exists  between  the  thirteen-year  and 
seventeen-year  races.  Two  or  three  of  the  States  have  but  one  brood 
each ;  but  in  Ohio  there  are  at  least  six  seventeen-year  broods,  and 
in  North  Carolina  one  thirteen-year  and  six  seventeen-year  broods. 
I  judge,  however,  from  the  reports  that  even  in  these  last-mentioned 
States,  there  are  but  few  places,  if  any,  where  more  than  three  broods 
overlap. 

I  have  not  seen  any  discussion  of  the  causes  that  have  produced  these 
broods,  but  if  we  may  believe  that  they  have  existed  for  a  thousand 
generations,  a  possible  if  not  a  probable  cause  is  found  in  the  unsettled 
conditions  of  climate  that  must  have  attended  the  breaking-up  of  the 
great  ice  period.  During  years  of  diminished  cold,  colonies  may  have 
taken  possession  of  regions  which  were  too  cold  for  their  development 
at  the  return  of  the  seventeen-year  period  when  the  offspring  should 
have  appeared;  and  still  some  of  the  benumbed  and  delayed  pupae 
may  have  survived,  making  their  appearance  one,  two,  three,  or  more 
years  later,  when  conditions  were  more  favorable.  The  following  ob- 
servation referred  to  by  Dr.  Riley,  in  explanation  of  the  accelerated 
or  retarded  appearance  of  sporadic  individuals,  throws  some  light 
on  the  origin  of  the  different  broods : 

That  circumstances  favorable  or  otherwise  may  accelerate  or  retard  their  devel- 
opment was  accidentally  proven  in  1868  by  Dr.  E.  S.  Hull,  of  Alton,  111.,  as  by  con- 
structing underground  flues  for  the  purpose  of  forcing  vegetables,  he  also  caused 
the  Cicadas  to  issue  as  early  as  the  20th  of  March,  and  at  consecutive  periods 
afterwards  till  May,  though,  strange  to  say,  these  premature  individuals  did  not 
sing.  They  frequently  appear  in  small  numbers,  and  more  rarely  in  large  num- 
bers, the  year  before  or  the  year  after  their  proper  period.  This  is  more  especially 
the  case  with  the  thirteen-year  broods.* 

That  climate  has  been  an  important  factor  in  the  development  of  the 
thirteen  and  seventeen  year  races  is  indicated  by  the  fact  that  most 
of  the  districts  occupied  by  the  seventeen-year  race  lie  north  of  latitude 


*  Bulletin  No.  8,  Division  of  Entomology,  U.  S.  Department  of  Agriculture,  p.  8. 


SEXUAIv   AND   CYCUCAIv  ISOIvATION.  233 

38°,  and  most  of  those  occupied  by  the  thirteen-year  race  He  south  of 
that  Une,  though  in  lUinois  there  is  a  thirteen-year  brood  as  far  north 
as  latitude  40°.  Dr.  Riley  has  not  referred  to  the  coincidence,  but  it 
seems  to  me  a  fact  of  some  interest  in  this  connection  that  the  southern 
limit  of  the  great  ice-cap  which  covered  Canada  and  the  northern  part 
of  the  United  States  during  the  glacial  epoch  extended  along  an  irreg- 
ular line  between  the  parallels  of  latitude  38°  and  40°.  Lying  south 
of  the  ice  region  there  was  probably  a  considerable  belt  of  country  cov- 
ered with  pines  and  other  conifers  not  adapted  to  the  breeding  of  this 
species,  so  that  both  races,  if  they  then  existed,  must  have  been 
crowded  into  the  southern  portion  of  the  region  now  occupied  by  the 
thirteen- year  race. 

Instinctive  and  cyclical  forms  of  isolation,  such  as  cause  the  inde- 
pendent generation  of  the  races  and  broods  of  this  species,  are  usually 
associated  with  clearly  developed  specific  distinctions  relating  to  form, 
color,  and  function.  This  does  not,  however,  prove  that  the  isola- 
tive  divergence  was  subsequent  to  the  general  divergence  in  other  re- 
spects. The  number  of  generations  covered  by  the  initial  stage  in 
which  the  different  sections  are  only  races  is  very  small  compared  with 
those  that  are  likely  to  be  covered  by  the  stages  when  they  are  separate 
species  and  genera.  It  is  only,  therefore,  by  rare  chance  that  we  find  two 
forms  that  are  still  in  the  earliest  stage  of  palpable  divergence  and  are, 
at  the  same  time,  completely  segregated  by  constitutional  differences. 
Again,  segregative  endowments  are  usually  developed  somewhat  grad- 
ually; and  while  the  segregation  is  advancing  other  transformations 
take  place,  so  that  by  the  time  all  crossing  has  come  to  an  end  the  dif- 
ferent sections  have  become  well-marked  species.  Sometimes,  as  in 
the  three  species  of  butterflies  already  considered,  there  is  more  or  less 
crossing  after  the  sections  have  become  quite  distinct  species.  Such 
cases,  however,  as  are  presented  by  the  thirteen-year  and  seventeen-year 
races  and  by  the  different  broods  of  this  species  of  Cicada  show  that 
complete  segregation  may  be  produced  by  the  psychological  and  physio- 
logical constitution  of  different  races,  while  distinctions  of  form,  color 
and  manner  of  call  are  entirely  wanting  so  far  as  we  can  observe. 
This  has  seemed  impossible  to  some  naturalists,  especially  since  Dar- 
win has  admitted  that  cross-sterility  can  not  be  attributed  to  natural 
selection,  and  has,  therefore,  attributed  it  to  the  indirect  effects  of 
other  qualities  which  have  been  produced  by  natural  selection. 
.  The  great  contrast  in  this  respect  between  the  species  of  Basilarchia 
and  the  thirteen-year  and  seventeen- year  races  of  the  periodical  cicada 
may  perhaps  be  partially  explained  by  the  fact  that  the  latter  spend 
the  greater  part  of  their  existence  under  ground,  where  the  conditions 


234  APPENDIX   II — INTENSIVE    SEGREGATION. 

have  not  been  seriously  changed  since  the  close  of  the  last  glacial 
period.  Again,  one  generation  of  the  seventeen-year  race  of  Cicada 
covers  many  generations  of  the  Basilarchia,  bringing  thirty  or  forty 
fluctuations  of  climate,  food,  etc., to  the  latter,  while  the  former  is,  for 
the  most  part,  protected  from  serious  fluctuations. 

It  is  of  course  equally  impossible  to  prove  by  all  inclusive  observa- 
tions either  that  transformation  is  never  completely  parallel  in  sections 
of  a  species  that  are  prevented  from  crossing  or  that  independent  gene- 
ration long  continued  is  sure  to  result  in  independent  transformation, 
and,  therefore,  in  divergence;  but  it  is  of  no  small  interest  that  we 
find  in  the  thirteen-year  and  seventeen-year  races  of  this  species  the 
strongest  proof  that  there  are  sometimes  divergences  which  our  senses 
do  not  perceive.  If  our  senses  were  a  sufficient  test,  it  might  be  main- 
tained that  between  these  races  a  high  degree  of  local  and  cyclical 
isolation  has  existed  for  many  generations,  without  any  other  form  of 
transformation  having  arisen  to  increase  the  divergence ;  but  if  our 
informants  are  correct  when  they  tell  us  that  these  races  do  not  cross 
when  appearing  in  the  same  district  and  at  the  same  time,  we  need  not 
hesitate  to  affirm  that  there  must  be  some  distinguishing  character- 
istics by  which  those  of  one  race  are  able  to  find  each  other,  as  well 
as  segregative  instincts  which  lead  them  to  choose  each  other's 
society;  and,  even  if  our  informants  are  mistaken  in  supposing  that 
cross-unions  do  not  occur,  there  must  be  some  form  of  incompatibility 
between  the  two  races,  resting  on  divergent  endowments;  for  other- 
wise we  should  find  hybrid  descendants  with  periods  of  more  than 
thirteen  and  less  than  seventeen  years'  duration. 

IV.  CoNci,UDiNG  Remarks. 

1.  Outline  of  the  Argument  in  Support  of  the  Theory  of  Divergent  Evolution 
through  Cumulative  Segregation. 

(i)  The  invariable  experience  of  mankind  in  producing  domestic 
races  shows  that  segregation  is  a  controlling  factor.  The  segregation 
that  produces  domestic  breeds  and  races  is  found  to  be  of  two  kinds : 
first,  that  which  is  produced  by  men  who  designedly  preserve  the 
different  styles  of  variation  presented  by  one  species,  while  at  the 
same  time  they  prevent  them  from  crossing ;  and,  second,  that  which 
commences  in  the  indiscriminate  division  of  the  species  into  sections 
that  are  prevented  from  freely  crossing  through  their  being  under  the 
care  of  separate  tribes  of  men,  and  which  is  changed  into  decided 
segregation  through  the  diversity  of  selection,  or  of  some  other  trans- 
forming principle,  to  which  the  different  sections  are  sure  to  be 


OUTUNB   OF  THE   ARGUMENT.  235 

expKJsed ;  for  it  is  found  that  these  principles  when  brought  to  bear 
on  separated  sections  never  produce  completely  parallel  effects. 

(2)  The  paramount  effects  of  independent  generation  having  been 
shown  in  the  broad  fields  of  biological  experiment  presented  by  the 
domestication  of  plants  and  animals,  the  question  is  next  raised 
whether  species  in  a  state  of  nature  are  subjected  to  influences  divid- 
ing the  individuals  of  one  species  into  sections  that  are  prevented 
from  crossing;  and,  if  they  are,  how  far  this  independent  generation 
involves  segregate  generation. 

In  my  paper  entitled  "Divergent  Evolution  through  Cumulative 
Segregation,"  it  was  shown  that  there  are  many  classes  of  activities 
by  which  the  individuals  of  a  species  are  thus  divided,  and  that,  in 
the  majority  of  cases,  the  very  process  that  separates  them  assorts 
them  into  classes  with  reference  to  one  or  more  points  of  character; 
thus  producing  segregation  that  is  similar  in  its  character  to  the  seg- 
regation that  is  designedly  produced  by  the  pigeon-fancier  between 
his  various  breeds  of  pigeons. 

In  the  earlier  half  of  the  present  paper  I  have  shown  that  the 
planting  of  a  small  colony,  resulting  from  migration  or  other  causes, 
inevitably  involves  some  segregation;  and  whenever  the  transform- 
ing influences  of  the  other  factors  of  evolution  begin  to  operate  in  the 
different  sections,  this  initial  segregation  is  inevitably  intensified  and 
the  divergence  increased ;  for  it  is  in  the  last  degree  improbable  that 
change  produced  by  these  principles  of  transformation  in  sections 
that  are  prevented  from  crossing  should  be  completely  parallel  in  the 
different  sections,  even  when  exposed  to  the  same  environment. 

(3)  The  last  step  is  to  show,  as  has  been  attempted  in  the  latter 
half  of  the  present  paper,  that  the  relations  to  each  other  of  varieties, 
species,  genera,  and  the  higher  groups  are  such  as  would  necessarily 
be  presented  if  all  such  differences  were  the  result  of  evolution  that  is 
always  dependent  on  some  form  of  segregation,  but  not  always  on 
diversity  of  natural  selection,  which  is  produced  by  exposure  to 
different  environments. 

We  have  found  that  persistent  differences,  whether  varietal,  specific, 
or  generic,  are  not  all  adaptational,  for  some  of  them  have  no  relation 
to  utility,  and  that  adaptational  differences  are  not  all  advantageous, 
for  some  of  them  relate  to  adaptations  that  would  meet  with  equal 
success  if  the  organisms  should  exchange  habitats,  but  that  in  every 
case  divergence,  whether  utilitarian  or  non-utilitarian,  whether  advan- 
tageous or  disadvantageous,  is  not  maintained  without  independent 
generation. 


236  APPENDIX   II — INTENSIVE   SEGREGATION. 

2.  Reply  to  Criticism. 

In  view  of  the  examples  of  divergence  that  have  been  discussed  in 
this  paper,  I  think  I  may  state,  as  in  my  previous  paper,  "It  is, 
therefore,  evident,  that  the  simple  fact  of  divergence  in  any  case  is 
not  sufficient  ground  for  assuming  that  the  divergent  form  has  an 
advantage  over  the  type  from  which  it  diverges."*  Mr.  Wallace 
has  criticized  this  statement,  f  using  the  following  words : 

It  seems  to  me  that  throughout  his  paper  Mr.  Gulick  omits  the  consideration  of 
the  inevitable  agency  of  natural  selection,  arising  from  the  fact  of  only  a  very 
small  proportion  of  the  offspring  produced  each  year  possibly  surviving.  *  *  * 
He  omits  from  all  consideration  the  fact  that  at  each  step  of  the  divergence  there 
was  necessarily  selection  of  the  fit  and  less  fit  to  survive;  and  that  if,  as  a  fact, 
the  two  extremes  have  survived,  and  not  the  intermediate  steps  that  led  to  one  or 
both  of  them,  it  is  a  proof  that  both  had  an  advantage  over  the  original  less  special- 
ized form. 

But  what  if  the  type  from  which  the  new  form  diverges  is  surviving  at 
the  same  time  that  the  new  form  survives  ?  And  what  if  both  the  forms 
are  surrounded  by  the  same  environment  which  they  use  in  different 
ways?  Where,  then,  is  the  proof  that  the  newer  form  has  an  advan- 
tage over  the  older  form  ?  This  was  the  class  of  facts  I  had  been  consider- 
ing in  the  preceding  paragraphs,  which  led  to  the  conclusion  criti- 
cized by  Mr.  Wallace ;  and  instead  of  omitting  ' '  the  consideration  of 
the  inevitable  agency  of  selection,"  it  was  the  very  thing  I  was  con- 
sidering. I  had  pointed  out  that  when  a  segregated  portion  of  a 
species  exposed  to  the  same  environment  changes  its  habits,  learning 
to  appropriate  resources  that  had  not  been  previously  used,  it  be- 
comes a  new  intergenerating  group  "m  which  a  new  and  divergent 
form  of  selection  is  established,"  but  that  the  result  of  the  divergence 
thus  produced  is  not  necessarily  advantageous,  and  may  for  many 
generations  be  somewhat  disadvantageous.  As  I  was  aware  that 
many  naturalists  would  consider  it  absurd  to  suppose  that  disadvan- 
tageous or  even  non-advantageous  instincts  ever  persist  and  become 
the  occasion  of  divergent  selection,  I  referred  to  Darwin's  opinion 
that  such  might  be  the  case  with  sexual  instincts,  and  that  the  pro- 
genitors of  man  were  deprived  of  their  hairy  coat  by  sexual  selection 
that  was,  in  its  earlier  stages,  disadvantageous.  I  am  not  aware  that 
Darwin  has  ever  attempted  to  show  how  divergent  sexual  instincts 
arise  and  become  permanently  fixed  as  distinguishing  characters  of 
varieties  and  species. 


*  Linnean  Society's  Journal,  Zoology,  vol.  xx,  p.  214. 
t  Nature,  vol.  xxxviii,  p.  491. 


RKPI.Y   TO   CKITICISM.  237 

"The  advantage  of  divergence,"  the  principle  on  which  he  relied  to 
account  for  divergent  habits,  producing  divergent  natural  selection, 
he  never  attempted  to  apply  here ;  and,  above  all,  when  he  believed 
the  newer  instincts  to  be  either  non-advantageous  or  disadvantageous 
as  contrasted  with  the  older  instincts,  he  certainly  could  not  have 
attributed  advantage  to  the  resulting  divergence.  As  I  have  pointed 
out  on  previous  occasions,  Darwin  assumed  a  psychological  divergence 
in  the  sexual  instincts  of  a  species  in  order  to  account  for  the  diver- 
gence in  their  secondary  sexual  pharacters  relating  to  form,  color,  etc. ; 
and  as  there  is  no  reason  given  why  the  psychological  divergence 
should  take  place,  or  why  it  should  precede  the  change  in  form  and 
color,  the  theory  of  sexual  selection,  as  presented  by  Darwin,  is  in- 
complete, especially  in  its  relations  to  divergent  evolution.  If  he 
had  thrown  light  on  the  causes  of  divergence  in  sexual  instincts,  he 
would  have  found  the  same  or  similar  principles  applicable  to  the 
explanation  of  divergence  of  all  kinds.  But  my  object  in  referring 
to  his  opinion  here  is  to  point  out  that  he  was  free  to  admit  that  per- 
manent divergence  in  sexual  instincts. may  be  non-advantageous,  or 
even  somewhat  disadvantageous ;  and  if  this  is  true  of  sexual  instincts, 
I  do  not  see  why  it  may  not  be  equally  true  of  industrial  instincts.  I 
think  there  is  ample  evidence  that,  when  segregation  has  been  estab- 
lished, divergence  which  is  neither  advantageous  nor  disadvantageous 
often  arises  in  industrial  as  well  as  other  instincts,  and  that  these  in- 
stincts may  introduce  new  forms  of  environal,  sexual,  or  social  selec- 
tion. The  relations  which  exist  between  habits  and  their  objects  are 
in  many  species  constantly  varying  in  such  a  way  as  to  constitute  a 
series  of  experiments;  and  when  independent  generation  exists  be- 
tween different  sections  of  a  species,  there  is  nothing  to  prevent  diver- 
gence in  the  results  of  those  experiments  in  the  different  sections,  even 
when  exposed  to  the  same  environment. 

In  Darwin's  "Posthumous  Essay  on  Instinct,"  published  as  an 
appendix  to  Romanes's  "Mental  Evolution  in  Animals,"  on  pages  378 
to  384,  mention  is  made  of  certain  "imperfections  and  mistakes  of 
instinct,"  and  of  certain  instincts  "that  are  carried  to  an  injurious 
excess,"  and  of  others  that  are  "small  and  trifling."  Of  the  last- 
named  he  says : 

I  have  not  rarely  felt  that  small  and  trifling  instincts  were  a  greater  diflicully  in 
our  theory  than  those  which  have  so  justly  excited  the  wonder  of  mankind;  for  an 
instinct,  if  really  of  no  considerable  importance  in  the  struggle  for  life,  could  not 
be  modified  or  formed  through  natural  selection. 

After  mentioning  several  which  might  perhaps  be  considered  tri- 
fling but  are  really  of  great  importance  to  the  species,  he  alludes  to  a 


238  APPENDIX  II — INTENSIVE   SEGREGATION. 

few  that  seem  to  be  "mere  tricks"  or  "habits  without  use  to  the  ani- 
mals." Mr.  Romanes,  referring  to  these  cases,  offers  the  following 
explanation  on  page  275  of  the  same  work  (I  quote  from  the  New 
York  edition,  Appleton  &  Co.,  1884) : 

We  have  seen  abundant  evidence  that  non-adaptive  habits  occur  in  individuals, 

and  may  be  inherited  in  the  race.     Therefore,  if  from  play,  affection,  curiosity,  or 

even  mere  caprice,  the  animal  should  perform  any  useless  kind  of  action  habitually 

and  if  this  habit  were  to  become  hereditary  in  the  similarly  constituted 

progeny,  we  should  have  a  trivial  or  useless  instinct. 

As  an  example  of  a  strongly  inherited  non-adaptive  instinct  in  a 
wild  creature  may  be  mentioned  the  cackling  of  the  wild  hen  of  India 
after  having  laid  an  egg.  This  habit  is  referred  to  by  Darwin  as  one  that 
may  be  slightly  detrimental ;  but  all  that  is  necessary  to  put  it  beyond 
the  developing  influence  of  natural  selection  is  that  it  should  fail  of 
bringing  advantage  to  the  species ;  and  that  it  is  of  no  advantage  will, 
I  think,  be  generally  admitted.  If,  then,  species  differ  in  regard  to 
instincts  that  are  non-advantageous,  they  are  liable  to  present  non- 
advantageous  differences  in  form  and  color,  resulting  either  from  the 
same  causes  that  have  produced  the  divergent  instincts,  or  from 
divergent  forms  of  environal,  sexual,  and  social  selection  produced  by 
these  instincts ;  it  will,  however,  be  found  that  segregate  intergenera- 
tion  is  the  necessary  condition  on  which  the  divergence  of  innate 
characters  depends. 

In  the  present  paper  and  in  other  places  I  have  mentioned  cases, 
representative  of  multitudes  of  others,  in  which  there  is  divergence 
between  two  varieties  or  species  occupying  different  districts,  but 
surrounded  by  the  same  environment.  In  such  cases  the  differ- 
ences presented  by  the  separate  forms,  and  the  divergence  by  which 
the  differences  have  been  produced,  can  not  be  regarded  as  advan- 
tageous ;  for  if  the  forms  should  exchange  districts,  the  environment 
being  the  same,  no  disadvantage  would  be  experienced;  and  this  is 
equally  true  whether  the  differences  relate  to  industrial  adaptations 
or  to  adaptations  between  the  sexual  instincts  and  the  secondary 
sexual  characters  of  the  group,  or  to  characters  that  are  absolutely 
non-utilitarian. 

Mr.  Wallace  says  that  in  my  previous  paper  he  looks  in  vain  for 
any  proof  that  cumulative  segregation  produces  cumulative  diver- 
gence ;  but  at  the  same  time  he  claims  that  the  segregation  of  which  I 
speak,  and  which  I  have  illustrated  by  a  supposed  case  in  the  breeding 
of  pigeons,  is  a  form  of  selection  which  he  calls  "selection  by  separa- 
tion." Adopting  his  phrase  for  the  moment,  I  understand  that  he 
fully  admits  that  in  domestication  "selection  by  separation"  will 


CUMULATIVE   SEGREGATION   AND   DIVERGENCE.  239 

produce  divergence.  Does  he  then  doubt  that  the  same  process  pro- 
duced by  natural  causes  will  result  in  divergence?  Or  does  he  deny 
that  "selection  by  separation"  ever  takes  place  in  nature?  He  will 
probably  grant  that  wherever  natural  causes  act  upon  the  repre- 
sentatives of  a  species  in  such  a  way  that  in  each  generation  those 
presenting  one  style  of  variation  are  led  to  breed  together  and  are 
prevented  from  breeding  with  other  kinds,  there  divergence  will  cer- 
tainly follow.  This  is  what  I  call  "segregation."  That  without  it 
there  is  no  cumulative  divergence,  and  that  with  it  there  is  always 
divergence,  is  amply  proved  by  the  universal  experience  of  man  in 
the  domestication  of  plants  and  animals.  All  that  is  lacking  is  the 
consistent  application  of  our  knowledge  to  the  theory  of  evolution. 

Segregation  is  a  process  of  much  deeper  significance  than  indis- 
criminate isolation,  with  which  he  seems  to  confound  it,  and  one 
which  in  nature  arises  from  a  wide  range  of  causes,  some  of  which  I 
have  pointed  out.  But  isolation  without  assortment  of  the  forms 
according  to  any  principle  by  which  those  of  a  kind  are  brought  to- 
gether is  often  transformed  into  segregation  by  the  operation  of  the 
principles  of  transformation  in  the  isolated  sections  of  the  species. 
This  change  is  often  brought  about  by  the  difference  of  the  environ- 
ments to  which  the  organism  is  exposed  in  the  isolated  areas.  This 
one  form  of  segregation  has  been  clearly  pointed  out  by  Darwin, 
though  he  did  not  recognize  segregation  as  a  necessary  condition  for 
divergence.  There  are,  however,  many  other  ways  in  which  nature 
produces  a  similar  result.  Some  of  these  are  operative  when  the 
organism  is  distributed  in  isolated  districts  but  surrounded  by  the 
same  environment,  and  some  of  them  have  to  do  with  the  develop- 
ment of  non-adaptative  divergences,  which  can  not  come  under  the 
cumulative  influence  of  natural  selection. 

It  thus  appears  that  independent  generation  cooperating  with 
natural  selection  is  one  form  of  the  wider  principle  of  segregation 
which,  in  its  many  forms,  is  the  ever-present  condition  preceding 
cumulative  divergence.  Whatever  divides  the  representatives  of  a 
species  in  such  a  way  that  those  of  a  kind  are  made  to  intergenerate 
while  prevented  from  intergenerating  with  other  kinds  is  a  cause  of 
segregation.  This  is  my  definition  of  segregation,  and  my  theory  is 
that  whatever  causes  segregation  causes  divergence,  and  without 
segregation  there  is  no  cumulative  divergence.  Now,  in  order  to  refute 
the  theory  it  is  necessary  to  show  either  that  segregation  does  not  take 
place  in  nature  or  that  it  is  not  accompanied  by  divergence,  or  that  diver- 
gence takes  place  without  segregation.  As  Mr.  Wallace  has  not  at- 
tempted to  prove  any  one  of  these  counter  propositions,  I  think  his 


240  APPENDIX   II — INTENSIVE   SEGREGATION.      , 

criticism  is  aside  from  the  main  issue.  Even  if  my  paper  presents  "a 
body  of  theoretical  statements"  with  "no  additional  facts,"  this  does 
not  show  that  the  theory  is  incorrect  or  the  new  use  of  the  old  facts 
unimportant  in  the  explanation  of  divergent  evolution.  "The 
Origin  of  Species"  was  filled  with  new  theories  applied  to  old  facts. 
The  importance  of  cumulative  divergence  through  cumulative  segre- 
gation, if  a  fact,  is  admitted.  Is  it  a  fact?  is  then  the  question  that 
needs  to  be  discussed.  If,  however,  segregation  is  assumed  to  be  the 
isolation  of  sections  of  a  species  possessing  exactly  the  same  average 
character,  the  assumption  will  be  contrary  to  the  facts  that  usually 
exist,  even  in  cases  of  indiscriminate  isolation. 

In  the  Journal  of  the  Royal  Microscopical  Society,  1889,  part  i, 
pages  33-34,  will  be  found  an  appreciative,  though  a  very  brief 
review  of  my  theory,  closing  with  the  suggestion  that  fuller  elucida- 
tion is  needed  of  the  alleged  tendency  in  nature  to  transform  separa- 
tion, when  long  continued,  into  increasing  segregation  and  divergence. 
Want  of  space  in  my  first  essay  made  it  necessary  to  postpone  the  full 
discussion  of  this  part  of  the  theory,  but  in  the  present  paper  I 
have  sought  to  point  out  some  of  the  more  manifest  principles  on 
which  this  general  law  of  intension  rests.  There  are  undoubtedly 
other  principles  of  transformation,  which,  when  combined  with 
separate  breeding,  inevitably  produce  divergent  instead  of  parallel 
evolution ;  but  the  principles  pointed  out  in  this  paper  are  sufficient 
to  establish  the  general  tendency  and  to  show  that  natural  selection 
is  by  no  means  the  only  principle  on  which  the  law  rests.  If  we  could 
obtain  sections  of  a  species  presenting  exactly  the  same  average  char- 
acter, and  if  we  could  prevent  all  the  principles  of  transformation 
from  coming  in  to  aid  in  the  process,  separate  breeding  under  such 
conditions  would  perhaps  never  produce  divergence ;  but,  as  separa- 
tion never  produces  exactly  equivalent  sections,  it  always  tends  to 
introduce  transformation,  through  changed  or  unbalanced  action, 
and  transformation  in  the  separated  sections  inevitably  becomes 
divergence.  We  thus  gain  an  explanation  of  the  fact  that  isolation, 
even  when  accompanied  by  exposure  to  the  same  environment,  if  long 
continued,  always  introduces  divergent  forms  of  selection.  Indepen- 
dent generation  precedes  and  determines  the  possibility  of  the  diver- 
gence, and  if  it  is  segregative  it  also  determines  in  a  measure  the  form 
of  the  divergence ;  but  even  if  it  is  simply  separative,  it  involves  the 
complete  cessation  of  all  forms  of  reflexive  selection  maintaining 
compatibility  between  the  isolated  sections,  and,  therefore,  opens  the 
way  for  the  gradual  entrance  of  divergent  forms,  first  of  reflexive,  and 
then  of  environal  selection. 


CONSTRUCTION   OF  THE   PERMUTATIONAL  TRIANGLE.  24 1 

3.  Construction  of  the  Pertnutational  Triangle, 

In  my  paper  on  ' '  Divergent  Evolution  "*  I  referred  to  the  permuta- 
tional  triangle,  which  I  had  constructed  in  order  to  determine  the  prob- 
ability of  extinction  that  would,  under  certain  conditions,  result  from 
complete  segregate  fecundity,  when  unaided  by  any  form  of  positive 
segregation.  The  first  four  lines  of  the  table  were  obtained  by  direct 
observation  on  the  permutations  of  letters  arranged  to  represent  the 
pairing  of  animals  entirely  lacking  in  instincts  or  qualities  that  secure 
the  pairing  together  of  those  of  one  kind. 

For  example,  let  A,  B,  C  represent  three  females  of  three  varieties 
of  pigeons,  and  a,  h,  c  three  males  of  the  same  varieties,  all  occupying 
one  aviary.  Now,  supposing  they  are  devoid  of  segregating  instincts, 
and  that  they  all  pair,  what  are  the  probabilities  concerning  the  pair- 
ing of  the  males  with  their  own  kind  ?  These  will  be  clearly  shown  by 
arranging  the  letters  representing  one  of  the  sexes  in  one  fixed  order, 
placing  the  letters  representing  the  other  sex  underneath  in  every 
possible  permutation  of  order.  If  we  make  six  experiments  the  proba- 
bility is  that  in  two  cases  none,  in  three  cases  one, 
in  no  case  two,  and  in  one  case  three,  will  pair  with 
their  own  kind.  These  numbers  constitute  the 
four  terms  of  the  third  line.  The  first,  second, 
and  fourth  lines  were  constructed  in  the  same  way, 
but  for  the  construction  of  the  tenth  line  in  this 
way  I  estimated  that  several  years  of  constant 
writing  would  be  required.  The  remaining  lines 
here  given  were,  therefore,  constructed  according 
to  the  following  rules,  which  were  discovered  by  studying  the  first 
four  lines.  The  discussion  of  different  methods  of  constructing  the 
permutational  triangle,  and  the  interesting  properties  of  the  same 
when  constructed,  must  be  deferred;  but  I  may  say  here  that  I 
believe  it  will  be  found  an  important  instrument  for  estimating  a  large 
class  of  probabilities. 

One  method  of  constructing  any  line  of  the  permutational  triangle  from 
the  preceding  line. — (i)  Of  any  given  line,  any  desired  number,  except 
the  first,  may  be  obtained  by  multiplying  the  preceding  number  of  the 
preceding  line  by  the  factor  of  the  given  line  and  dividing  the  result  by 
the  figure  marking  the  degree  of  correspondence  of  the  column  of  the 
desired  number.  (2)  The  first  number  of  any  line  is  one  less  or  one 
more  than  the  second  number  of  the  same  line,  according  as  the  factor 
of  the  line  is  an  odd  or  an  even  number. 


A 

B 

C 

a 

b 

c 

a 

c 

b 

c 

a 

b 

b 

a 

c 

b 

c 

a 

c 

b 

a 

*  Also  see  pp.  99-100  of  this  volume. 


242 


APPENDIX   II — INTENSIVE   SEGREGATION. 


A  method  of  constructing  the  permutitional  triangle  from  the  arithmet- 
ical triangle. — Pascal's  arithmetical  triangle,  which  is  the  same  as  the 
table  of  binomial  coefficients,  is  a  series  of  figures,  each  line  of  which 
may  be  formed  by  adding  the  previous  line  to  itself,  as  shown  in  the 
table  below.  Now,  if  we  compare  this  arithmetical  triangle  with  my 
permutational  triangle  we  find  that  the  first  and  third  diagonal  lines 
in  each  table  are  composed  of  the  same  numbers  arranged  in  the  same 
way.  The  fourth  diagonal  line  of  the  permutational  triangle  can  be 
obtained  by  multiplying  each  number  of  the  arithmetical  triangle  by  2  • 


Multipliers 


In  short,  by  using  the  numbers  here  indicated  as  multipliers,  each 
line  of  the  arithmetical  triangle  may  be  transformed  into  the  corre- 
sponding line  of  the  permutational  triangle.  It  may  further  be  noted 
that  these  numbers  by  which  we  multiply  are  the  occurrents  standing 
in  the  first  column  of  the  permutational  triangle ;  and  these  are  found 
to  be  the  same  as  the  sub-factorials  described  by  Whit  worth  in 
"Choice  and  Chance,"  Chapter  IV. 


THE   PERMUTATIONAL  TRIANGLE. 


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11 

APPENDIX  III. 

LETTERS  PUBLISHED  IN   NATURE. 
I.  "Like  to  Like" — A  FundamentaIv  Principle  in  Bionomics.* 

I  follow  Professor  Lankester  in  the  use  of  the  terra  bionomics  to 
designate  the  science  treating  of  the  relations  of  species  to  species.  If 
the  theory  of  evolution  is  true,  bionomics  should  treat  of  the  origin 
not  only  of  species  but  of  genera,  and  the  higher  groups  in  which  the 
organic  world  now  exists. 

In  Professor  Lankester's  very  suggestive  review  of  "Darwinism," 
by  Mr.  A.  R.  Wallace  (Nature,  October  lo,  1889,  p.  566),  reference  is 
made  to  "his  (Mr.  Wallace's)  theory  of  the  importance  of  the  principle 
of  'like  to  like'  in  the  segregation  of  varieties,  and  the  consequent 
development  of  new  species."  Professor  I^ankester  has  here  alluded 
to  a  principle  which  I  consider  more  fundamental  than  natural  selection, 
in  that  it  not  only  explains  whatever  influence  natural  selection  has  in  the 
formation  of  new  species,  but  also  indicates  combinations  of  causes  that 
may  produce  new  species  without  the  aid  of  diversity  of  natural  selection. 
The  form  of  like  to  like  which  Mr.  Wallace  discusses  is  "the  constant 
preference  of  animals  for  their  like,  even  in  the  case  of  slightly  different 
varieties  of  the  same  species,"  which  is  considered  not  as  an  independ- 
ent cause  of  divergence,  but  as  producing  isolation  which  facilitates 
the  action  of  natural  selection.  If  he  had  recognized  this  principle, 
which  he  calls  selective  association,  as  capable  of  producing  in  one 
phase  of  its  action  sexual  and  social  segregation,  and  in  another  phase 
sexual  and  social  selection,  he  would  perhaps  have  seen  that  its  power 
to  produce  divergence  does  not  depend  on  its  being  aided  by  natural 
selection. 

Mr.  Wallace's  view  is  very  clearly  expressed  in  the  following  pass- 
ages, though  I  find  other  passages  which  lead  me  to  think  that  the 
chief  reason  he  does  not  recognize  segregation  as  the  fundamental  prin- 
ciple in  divergence  is  that  he  has  not  observed  its  relations  to  the  prin- 
ciple of  like  to  like.  He  says:  "Agreatbody  of  facts  on  the  one  hand, 
and  some  weighty  arguments  on  the  other,  alike  prove  that  specific 
characters  have  been,  and  could  only  have  been,  developed  and  fixed 
by  natural  selection  because  of  their  utility."  (Darwinism,  p.  142.) 
"Most  writers  on  the  subject  consider  the  isolation  of  a  portion  of  a 
species  a  very  important  factor  in  the  formation  of  new  species,  while 


*  Published  in  Nature,  April  10,  1890. 

245 


246  APPENDIX  III — I.ETTERS   PUBUSHED   IN   NATURE. 

others  maintain  it  to  be  absolutely  essential.  This  latter  view  has 
arisen  from  an  exaggerated  opinion  as  to  the  power  of  intercrossing  to 
keep  down  any  variety  or  incipient  species  and  merge  it  in  the  parent 
stock."     (Darwinism,  p.  144.) 

I  think  we  shall  reach  a  more  consistent  and  complete  apprehension 
of  the  subject  by  starting  with  the  fundamental  laws  of  heredity,  and 
refusing  to  admit  any  assumption  that  is  opposed  to  these  principles, 
till  sufficient  reasons  have  been  given.  Laws  which  have  been  estab- 
lished by  thousands  of  years  of  experiment  in  domesticating  plants 
and  animals  should  be,  it  seems  to  me,  consistently  applied  to  the  gen- 
eral theory  of  evolution.  For  example,  if  in  the  case  of  domesticated 
animals,  "it  is  only  by  isolation  and  pure  breeding  that  any  specially 
desired  qualities  can  be  increased  by  selection"  (see  Darwinism,  p.  99), 
why  is  not  the  same  condition  equally  essential  in  the  formation  of 
natural  varieties  and  species?  If  in  our  experiments  we  find  that 
careful  selection  of  divergent  variations  of  one  stock  does  not  result  in 
increasingly  divergent  varieties  unless  free  crossing  between  the  varieties 
is  prevented,  why  should  it  be  considered  an  exaggeration  to  hold  that 
in  wild  species  ' '  the  power  of  intercrossing  to  keep  down  any  variety 
or  incipient  species,  and  merge  it  in  the  parent  stock,"  is  the  same  that 
we  have  found  in  domestic  species.  Experience  shows  that  segrega- 
tion, which  is  the  bringing  of  like  to  like  in  groups  that  are  prevented  from 
crossing,  is  the  fundamental  principle  in  the  divergence  of  the  various 
forms  of  a  given  stock,  rather  than  selection,  which  is  like  to  like  through 
the  prevention  of  certain  forms  from  propagating;  and  I  think  we  intro- 
duce confusion,  perplexity,  and  a  network  of  inconsistencies  into  our 
exposition  of  the  subject  whenever  we  assume  that  the  latter  is  the 
fundamental  factor,  and  especially  when  we  assume  that  it  can  produce 
divergence  without  the  cooperation  of  any  cause  of  segregation  divid- 
ing the  forms  that  propagate  into  two  or  more  groups  of  similars,  or 
when  we  assume  that  segregation  and  divergence  can  not  be  produced 
without  the  aid  of  diverse  forms  of  selection  in  the  different  groups. 
The  theory  of  divergence  through  segregation  states  the  principle 
through  which  natural  selection  becomes  a  factor  promoting  some- 
times the  stability  and  sometimes  the  transformation  of  types,  but 
never  producing  divergent  transformation  except  as  it  cooperates  \\  ith 
some  form  of  isolation  in  producing  segregation ;  and  it  maintains  that 
whenever  variations  whose  ancestors  have  freely  intergenerated  are, 
from  any  combination  of  causes,  subjected  to  persistent  and  cumula- 
tive forms  of  segregation,  divergence  more  or  less  pronounced  must  be 
the  result.  The  laws  of  heredity  on  which  this  principle  rests  may  be 
given  in  the  three  following  statements. 


UKE   TO   UKE    — A  FUNDAMENTAI^  PRINCIPLE.  247 

1 .   The  Laws  of  Heredity. 

(i)  Unlike  to  unlike,  or  the  removal  of  positive  segregating  influ- 
ences, is  a  principle  that  results  either  in  extinction  through  failure 
to  propagate  or  in  the  breaking  down  of  divergences  through  free 
crossing. 

(2)  Like  to  like,  when  the  individuals  of  each  intergenerating 
group  represent  the  average  character  of  the  group,  is  a  principle 
through  which  the  stability  of  existing  types  is  promoted. 

(3)  Like  to  like,  when  the  individuals  of  each  group  represent  other 
than  the  average  character  of  the  group,  is  a  principle  through 
which  the  transformation  of  types  is  effected. 

2.  Local  Segregation  often  Initiates  Divergence,  which  Social,  Sexual, 
Industrial,  and  Impregnational  Segregation,  with  Corresponding  Forms 
of  Selection,  Carry  to  Completion. 

In  my  paper  on  "Divergent  Evolution"  I  pointed  out  that  sexual 
and  social  instincts  often  conspire  to  subdivide  a  species,  bringing  like 
to  like  in  groups  that  do  not  cross ;  and  that  in  such  cases  there  will  be 
divergence  even  when  there  is  no  diversity  of  natural  selection  in  the 
different  groups,  as,  for  example,  when  the  different  groups  occupy 
the  same  area  and  are  guided  by  the  same  habits  in  their  use  of  the 
environment.  There  is  reason  to  believe  that  under  such  circum- 
stances divergence  often  arises  somewhat  in  the  following  way :  Local 
segregation  of  a  partial  nature  results  in  some  diversity  of  color  or 
in  some  peculiar  development  of  accessory  plumes,  and  through  the 
principle  of  social  segregation  which  leads  animals  to  prefer  to  asso- 
ciate with  those  whose  appearance  has  become  familiar  to  them,  the 
variation  is  prevented  from  being  submerged  by  intercrossing. 
There  next  arises  a  double  process  of  sexual  and  social  selection, 
whereby  both  the  peculiar  external  character  and  the  internal  instinct 
that  leads  those  thus  characterized  to  associate  together  are  intensi- 
fied. The  instinct  is  intensified,  because  any  member  of  the  com- 
munity that  is  deficient  in  the  desire  to  keep  with  companions  of  that 
kind  will  stray  away  and  fail  of  breeding  with  the  rest.  This  process 
I  call  social  selection.  The  peculiarity  of  color  or  plumage  is  preserved 
and  accumulated,  because  any  individual  deficient  in  the  character- 
istic is  less  likely  to  succeed  in  pairing  and  leaving  progeny.  This 
latter  process  is  sexual  selection.  It  can  hardly  be  questioned  that 
both  these  principles  are  operative  in  producing  permanent  varieties 
and  initial  species;  and  in  the  circumstances  I  have  supposed  I  do 
not  see  how  the  process  can  be  attributed  to  natural  selection.  Varie- 
ties thus  segregated  may  often  develop  divergent  habits  in  their  use 


248  APPENDIX   III — LETTERS  PUBLISHED   IN   NATURE. 

of  the  environment,  resulting  in  divergent  forms  of  selection,  and  pro- 
ducing additional  changes ;  but  so  long  as  the  environment  and  their 
habits  of  using  the  environment  remain  unchanged,  their  diver- 
gences can  not  be  due  to  environal  selection  of  any  kind. 

Mr.  Wallace's  very  interesting  section  on  "Color  as  a  Means  of 
Recognition,"  taken  in  connection  with  the  section  on  "Selective 
Association,"  already  referred  to,  and  another  on  "Sexual  Characters 
due  to  Natural  Selection,"  offers  an  explanation  of  "the  curious  fact 
that  prominent  differences  of  color  often  distinguish  species  other- 
wise very  closely  allied  to  each  other  "  (p.  226).  His  exposition  differs 
from  mine  in  that  he  denies  the  influence  of  sexual  selection,  and  at- 
tributes the  whole  process  to  natural  selection,  on  the  ground  that 
"means  of  easy  recognition  must  be  of  vital  importance"  (p.  217). 
The  reasoning,  however,  seems  to  me  to  be  defective,  because  the 
general  necessity  for  means  of  easy  recognition  is  taken  as  equiva- 
lent to  the  necessity  for  a  specialization  of  recognition  marks  that 
shall  enable  the  different  varieties  to  avoid  crossing.  In  the  cases  I 
am  considering  there  is,  however,  no  advantage  either  for  the  indi- 
vidual or  the  species  in  the  separate  breeding  of  the  different  varieties, 
and  even  in  cases  where  there  is  such  an  advantage  for  the  species  (as 
there  would  be  if  the  variety  had  habits  enabling  it  to  escape  from 
competition  with  the  parent  stock,  but  not  preventing  it  from  cross- 
ing with  the  same),  it  does  not  appear  how  this  liability  to  breed  with 
the  original  stock  can  be  any  hindrance  to  the  success  of  the  individ- 
ual. The  significant  part  of  the  process  in  the  development  of  recog- 
nition marks  must  be  in  the  failure  of  such  individuals  to  secure  mates, 
which  is  sexual  selection ;  or  in  the  vmwillingness  of  the  community 
to  tolerate  the  company  of  such,  which  I  have  called  social  selection. 

3.  Permanent  Difference  in  Innate  Adaptations  not  Necessarily 
Advantageous  Difference. 

It  is  often  assumed  by  writers  on  evolution  that  permanent  differences 
in  the  methods  in  which  a  life- preserving  function  is  performed  are  neces- 
sarily useful  differences.  That  this  is  not  so  may  be  shown  by  an 
illustration  drawn  from  the  methods  of  language.  The  general  use- 
fulness of  language  is  most  apparent,  and  it  is  certain  that  some  of  the 
laws  of  linguistic  development  are  determined  by  a  principle  which 
may  be  called  "the  survival  of  the  fittest;"  but  it  is  equally  certain 
that  all  the  divergences  which  separate  languages  are  not  useful 
divergences.  That  one  race  of  men  count  by  tens  on  their  fingers  and 
another  by  twenties  on  their  fingers  and  toes,  is  not  determined  by 
differences  in  the  environments  of  the  races,  or  by  any  advantage 


UNSTABLE   ADJUSTMENTS   AND  ISOLATION.  249 

derived  from  the  difference  in  the  methods.  So,  easy  recognition  of 
other  members  of  the  species  is  of  the  highest  importance  for  every 
species ;  but  difference  in  ' '  recognition  marks ' '.  in  sections  of  the  same 
variety  separated  in  different  districts  of  the  same  environment  is  no 
advantage.  Under  the  same  conditions,  habits  of  feeding  may 
become  divergent ;  but,  since  any  new  habit  that  may  be  found  ad- 
vantageous in  one  district  would  be  of  equal  advantage  in  the  other 
district,  the  divergence  must  be  attributed  to  some  difference  in  the 
activities  of  the  two  portions  of  the  species. 

I  have  recently  observed  that,  of  two  closely  allied  species  of  flat- 
fish found  on  the  coasts  of  Japan,  one  always  has  its  eyes  on  the  right 
side  and  the  other  always  on  the  left.  As  either  arrangement  would 
be  equally  useful  in  the  environment  of  either  species,  the  divergence 
can  not  be  considered  advantageous. 

II.  Unstable  Adjustments  as  Affected  by  Isoi,ation.* 

In  a  brief  passage  in  his  volume  on  "Darwinism,"  Mr.  Wallace 
refers  to  a  principle  which  seems  to  me  to  be  worthy  of  much  wider 
application  than  he  has  given  to  it.  It  is  a  key  which  requires  only 
a  little  filing  to  prepare  it  for  unlocking  some  difficult  problems  in 
divergent  evolution.  Speaking  of  the  infertility  of  crosses,  he  says 
(p.  184): 

It  appears  as  if  fertility  depended  on  such  a  delicate  adjustment  of  the  male  and 
female  elements  to  each  other  that  unless  constantly  kept  up  by  the  preservation 
of  the  most  fertile  individuals,  sterility  is  always  ready  to  arise.  *  *  *  So 
long  as  a  species  remains  undivided,  and  in  occupation  of  a  continuous  area,  its 
fertility  is  kept  up  by  natural  selection;  but  the  moment  it  becomes  separated, 
either  by  geographical  or  selective  isolation  or  by  diversity  of  station  or  of  habits, 
then,  while  each  portion  must  be  kept  fertile  inter  se,  there  is  nothing  to  prevent 
infertility  arising  between  the  two  separated  portions. 

Here  is  an  application  of  the  principle  of  segregation  (or  of  like  to 
like  in  groups  that  do  not  cross)  in  which  indiscriminate  separation 
is  followed  by  increasing  divergence  in  the  different  portions,  not 
because  they  are  exposed  to  different  environments,  not  because  there 
is  any  advantage  in  such  divergence,  not  because  there  is  any  need 
that  the  function  should  be  performed  more  perfectly  in  one  portion 
than  in  the  other,  but  because  intergeneration,  which  is  the  principle 
by  which  correspondence  of  function  is  secured,  has  been  suspended 
for  some  generations ;  and,  in  the  absence  of  intergeneration,  neither 
natural  selection,  nor  any  other  principle,  is  capable  of  preserving 
complete  correspondence.     In  organisms   that  reproduce  sexually 


*  Published  in  Nature,  May  8,  1 890. 


250  APPENDIX   III — LETTERS   PUBLISHED   IN    NATURE. 

the  causes  of  divergence  are  all  causes  of  segregation ;  while  the  causes 
of  unification,  whether  of  functions  or  of  structures,  are  causes  of 
intergeneration.  If  the  environments  which  surround  the  isolated 
portions  are  the  same,  the  use  of  the  environment,  and,  therefore, 
the  forms  of  selection,  may  become  divergent;  if  the  use  continues 
unchanged,  some  useless  divergence  in  the  method  of  securing  the 
use  may  appear;  or,  if  all  the  relations  to  the  environment,  whether 
useful  or  useless,  remain  unchanged,  "the  adjustment  of  the  male  and 
female  elements  to  each  other"  are  liable  to  become  slightly  diver- 
gent, producing  mutual  infertility,  or  the  preference  of  the  sexes  for 
certain  shades  or  arrangements  of  color  in  their  mates  may  become 
slightly  diJBferent,  or,  through  some  slight  difference  in  the  hereditary 
elements  distributed  in  each  separated  portion  at  the  first,  one,  or  all 
of  these  causes  of  accumulated  divergence  may  be  introduced.  I 
think  it  is  evident  that  we  have  here  a  general  principle  which  is  as 
applicable  to  a  wide  range  of  divergences  as  it  is  to  the  divergence 
that  produces  mutual  infertility  and  sterility. 

The  context  shows  that  the  prominent  idea  in  Mr.  Wallace's  mind 
was  divergence  in  the  adjustment  of  the  male  and  female  elements, 
through  correlation  with  "some  diversity  of  form  or  color,"  resulting 
from  divergent  forms  of  natural  selection,  which  had  been  induced  by 
exposure  to  "somewhat  different  conditions  of  life."  But  if  the  rea- 
soning is  correct  in  the  sentences  I  have  quoted  above  it  gives  an 
explanation  of  similar  divergences  when  the  separated  portions  are 
exposed  to  the  same  environment  and  where  there  is  no  possible 
advantage  to  be  gained  by  divergence.  This  is  one  of  the  principles 
I  have  used  in  the  explanation  of  'the  divergences  of  Sandwich  Island 
land  mollusks ;  and  I  think  that  in  the  earlier  stages  of  the  develop- 
ment of  infertility  between  allied  forms  it  is  often  the  only  explana- 
tion that  is  applicable.  It  should,  however,  be  remembered  that,  for 
divergence  of  this  kind,  it  is  not  always  necessary  that  the  isolation 
should  be  either  complete  or  very  long  continued,  and  that,  when  the 
forms  that  are  not  fully  fertile  with  each  other  meet  and  more  or  less 
commingle,  there  is,  through  the  very  laws  of  propagation,  without 
any  aid  from  natural  selection,  a  constant  increase  in  the  ratio  of  the 
pure  breeds  to  the  mongrels,  and  an  accumulating  intensity  in  the 
segregative  instincts  and  the  physiological  incompatibilities.  As  this 
point  has  been  fully  discussed  in  my  paper  on  "Divergent  Evolu- 
tion," I  do  not  need  to  enlarge  on  it  here. 

There  is,  however,  another  phase  of  the  subject  which  is  indicated 
by  Mr.  Wallace's  suggestion  that  infertility  depends  on  "such  a 
delicate  adjustment"  that  it  is  more  easily  affected  by  isolation  than 


A  SINGIvB   PAIR   AND  THE   AVERAGE   CHARACTER.  25 1 

some  other  adjustments.  This  is,  I  think,  a  very  interesting  point, 
as  it  suggests  how  it  is  that,  in  some  cases  at  least,  physiological  diver- 
gence of  this  kind  is  one  of  the  first  forms  of  divergence  that  arises. 
But  in  some  species  other  adjustments  seem  to  be  more  delicate  than 
this,  and,  therefore,  more  easily  disturbed,  while  in  others  several 
sets  of  adjustments,  as  colors  and  other  recognition  marks  with  the 
preferences  that  correspond,  and  the  habits  of  feeding  and  defense, 
are  in  a  state  of  equilibrium,  the  stability  or  instability  of  which  is 
about  the  same  as  of  that  which  determines  the  relations  of  the  male 
and  female  elements.  In  this  last  class  of  cases  several  forms  of 
divergence  may  arise  during  the  same  stage  of  development,  and  that, 
too,  when  the  isolated  portions  are  exposed  to  the  same  environment. 
In  some  species  a  large  number  of  characters  are  in  a  state  of  unstable 
adjustment.  As  Professor  Lankester  has  suggested  near  the  close 
of  his  review  of  Wallace's  book,  this  cause  of  divergence  seems  to  be 
specially  operative  in  the  case  of  human  faculties.  But  variability 
with  plasticity  of  type  is  not  the  only  condition  that  affects  the  sta- 
bility of  segregated  portions  of  a  species.  Other  things  being  equal, 
a  single  pair  of  any  species  is  much  less  likely  to  represent  the  average 
of  all  the  characters  of  the  species  than  a  million  pairs.  This  consid- 
eration throws  light  on  the  comparative  lack  of  divergence  between 
the  land  animals  of  England  and  those  of  Ireland,  which  lack  has  been 
referred  to  by  Mr.  Wallace  as  an  objection  to  my  theory.  In  this 
case,  many  millions  of  some  of  the  species  were  probably  existing  in 
each  district  at  the  time  of  the  separation.  As  Professor  Lankester 
has  pointed  out,  the  representatives  of  the  human  species  in  the  two 
districts  have  somewhat  diverged;  and  the  probability  is  that,  if 
we  were  equally  acquainted  with  the  other  species,  we  should  find 
other  examples  of  divergence  in  minor  points.  If  the  isolation  is 
made  more  complete,  and  is  longer  continued,  I  believe  the  diver- 
gence will  gradually  become  more  apparent. 

Mr.  Wallace  has  mentioned  another  class  of  divergences,  which  he 
has  explained  as  due  to  surplus  energy  in  the  species,  ready  for  expen- 
diture in  ways  that  are  not  determined  by  conditions  in  the  environ- 
ment. I  maintain  that  through  unstable  adjustment  this  surplus 
naturally  takes  different  forms  when  the  species  is  divided  into  iso- 
lated groups;  and  Wallace  is  content  to  attribute  the  divergence  to 
individual  variability,  though  each  group  maintains  its  own  type. 
His  words  are : 

The  enormously  lengthened  plumes  of  the  bird  of  paradise  and  of  the  peacock 
must  be  rather  injurious  than  beneficial  in  the  bird's  ordinary  life.  The  fact  that 
they  have  been  developed  to  so  great  an  extent  in  a  few  species  is  an  indicatioti 


252  APPENDIX   III — LETTERS   PUBLISHED   IN   NATURE. 

of  such  perfect  adaptation  to  the  conditions  of  existence,  such  complete  success 
in  the  battle  of  life,  that  there  is,  in  the  adult  male  at  all  events,  a  surplus  of  strength, 
vitality,  and  growth  power,  which  is  able  to  expand  itself  in  this  way  without  injury. 
That  such  is  the  case  is  shown  by  the  great  abundance  of  most  of  the  species  which 
possess  iltese  wonderful  superfluities  of  plumage.  .  .  .  Why,  in  allied  species, 
the  development  of  accessory  plumes  Jias  taken  different  forms,  we  are  unable  to  say, 
except  that  it  may  be  due  to  that  individual  variability  which  has  served  as  the 
starting  point  for  so  much  that  seems  to  us  strange  in  form,  or  fantastic  in  color, 
both  in  the  animal  and  vegetable  world.*     (Darwinism,  p.  293.) 

It  is  no  small  gratification  to  me  that  Mr.  Wallace  has  found  this 
principle  of  unstable  adjustment  worthy  of  application  to  two  impor- 
tant classes  of  divergences;  and  that,  in  the  case  of  one  of  these 
classes,  he  has  recognized  that  correspondence  in  such  adjustments 
can  not  be  continuously  maintained  between  the  isolated  portions  of 
a  species.  I  trust  that  when  he  understands  the  relation  in  which 
instability  and  isolation  stand  to  each  other  in  my  theory  he  will 
admit  that  it  throws  some  light  on  the  remarkable  divergences  of 
Sandwich  Island  land  mollusks.  The  sub j ect  was  incidentally  touched 
upon  in  my  paper  on  "Divergent  Evolution  through  Cumulative 
Segregation"  (see  Appendix  I),  and  more  fully  discussed  in  the  sup- 
plemental paper  on  "Intensive  Segregation"  (see  Appendix  II). 

III.  Indiscriminate  Separation,  under  the  same  Environment,  a  Cause  of 

Divergence,  t 
1.  Divergence  Resulting  from  Isolation. 

I  have  accumulated  a  large  body  of  facts  indicating  that  separated 
fragments  of  a  species,  though  exposed  to  the  same  environment,  will 
in  time  become  divergent.  I  find  that,  wherever  a  species  possessing 
very  low  powers  of  migration  is  for  many  generations  divided  into  a 
series  of  fragments  by  barriers  that  do  not  obstruct  the  distribution 
of  surrounding  species,  more  or  less  divergence  arises  in  the  separated 
portions  of  the  species,  though,  in  the  same  areas,  there  is  no  diver- 
gence in  the  environing  species  whose  distribution  is  not  obstructed. 
I  still  further  find  that,  whenever  the  distances  intervening  between 
the  different  fragments  are  an  approximate  measure  of  the  time  and 
degree  of  separate  breeding  (as  is  frequently  the  case  as  long  as  the 
divergence  does  not  involve  any  physiological  and  psychological 
segregation),  these  distances  are  also  an  approximate  measure  of  the 
degree  of  divergence. 

.  The  validity  of  this  conclusion  is  called  in  question  because  it  is 
inconsistent  with  the  theory  that  all  divergence  is  due  to  diversity  of 


*  The  italicizing  is  mine^ 

t  Published  in  Natiu-e,  August  14,  1890. 


DIVERGENCE   RESULTING   FROM   ISOLATION.  253 

selection,  and  that  all  diversity  of  selection  is  due  to  exposure  to 
different  environments.  The  divergences  in  the  cases  above  referred 
to,  it  is  said,  are  probably  due  to  differences  in  the  environment  that 
are  not  easily  recognized.  This  was  the  explanation  suggested  by 
Darwin  when  the  facts  were  reported  to  him  in  1872.  The  division  of 
a  species  into  isolated  portions  did  not  seem  to  him  to  furnish  any 
factor  that  could  produce  divergence  unless  it  was  aided  by  exposure 
to  different  external  conditions.  The  same  view  is  expressed  in  his 
"Origin  of  Species,"  sixth  edition,  page  319. 

My  reply  is  twofold,  (i)  The  theory  that  all  divergences  in  Sand- 
wich Island  land  mollusks  are  due  to  differences  in  the  environment 
requires  us  to  believe  that  there  are  occult  influences  increasing  in 
difiference  with  each  additional  mile  of  separation,  and  that  these 
influences  control  the  natural  selection  of  the  mollusks,  but  have  no 
influence  on  any  other  species  occupying  the  same  areas.  A  theory 
that  involves  so  heavy  an  assumption  can  not  be  received  when  a 
simpler  theory  is  open  to  us.  (2)  I  believe  I  can  entirely  remove  this 
objection,  urged  against  my  conclusion  on  these  purely  theoretical 
grounds,  by  showing  that  there  are  certain  causes  of  divergence,  not 
depending  on  exposure  to  different  environments,  that  are  necessarily 
introduced  by  the  division  of  a  species  into  isolated  groups ;  and  that, 
under  the  influence  of  these  causes,  diversity  of  habits  may  arise  pro- 
ducing diversity  of  selection,  even  while  the  fragments  are  exposed  to 
the  same  environment. 

I  have  elsewhere  called  attention  to  the  fact  that  the  independent 
breeding  of  separated  groups,  as  far  as  we  can  judge,  always  tends  to 
produce  divergence ;  and  I  have  shown  that,  when  a  species  is  indis- 
criminately broken  into  independent  f ''agments,  the  tendency  to  diver- 
gence will,  on  the  average,  vary  in  direct  proportion  to  the  instability 
of  the  species  and  in  inverse  proportion  to  the  size  of  the  fragments ; 
for  on  these  factors  depends  the  probable  degree  of  departure  of  the 
average  character  of  the  fragment  from  the  average  character  of  the 
species  previous  to  its  being  broken  into  fragments,  and,  therefore, 
the  degree  of  segregation. 

I  wish  now  to  show  that  the  maintenance  of  certain  classes  of  char- 
acters always  belonging  to  an  unbroken  species  is  due  to  a  form  of 
selection  that  can  continue  only  so  long,  and  so  far,  as  free  crossing 
continues.  Reflexive  selection  is  a  formative  principle,  depending  on 
the  relations  in  which  the  members  of  an  intergenerating  group  of 
organisms  stand  to  each  other,  while  they  continue  to  intergenerate ; 
but  when  two  portions  of  an  original  species  have  become  so  divergent 
as  to  compete  with  each  other  in  the  same  area  without  crossing,  they 


254  APPENDIX    III — LETTERS    PUBLISHED   IN    NATURE. 

form  incipient  species,  and  each  belongs  to  the  environment  of  the  other. 
While  they  are  members  of  the  same  intergenerating  group,  their 
mutual  influence  results  in  reflexive  selection,  which  maintains  the 
correspondence  with  each  other  by  which  power  to  cross  is  preserved ; 
while  they  are  members  of  groups  that  do  not  cross,  their  mutual  influ- 
ence results  in  cumulative  segregation ;  for  it  inevitably  tends  toward 
the  preservation  of  variations  that,  through  greater  divergence,  best 
escape  from  competition.  I  have  elsewhere  defined  reflexive  selection 
as  being  the  exclusive  propagation  of  those  better  fitted  to  the  rela- 
tions in  which  the  members  of  the  same  species  stand  to  each  other, 
resulting  from  the  failure  to  propagate  of  those  less  fitted.  Among 
those  that  are  equally  fitted  to  the  environment  of  the  species,  and, 
therefore,  equally  preserved  by  natural  selection,  there  is  often  great 
difference  in  the  degrees  of  fitness  for  sustaining  such  relations  to  the 
rest  of  the  species  as  will  secure  an  opportunity  to  propagate.  To 
this  class  of  influences  belong  the  different  forms  of  sexual  selection 
through  which  the  sexual  instincts  and  the  correlated  sexual  charac- 
ters of  the  different  sexes  are  kept  in  full  coordination.  In  like  man- 
ner we  must  believe  that  the  pollen  of  any  species  is  kept  up  to  its  full 
degree  of  potency  by  the  constant  selection  which  results  from  the 
failure  to  propagate  of  the  individuals  whose  pollen  is  less  potent  or 
whose  germs  are  more  difficult  to  fertilize  than  the  average.  We  call 
this  potential  selection.  Again,  there  is  a  constant  selection  of  ani- 
mals that  are  suitably  endowed  with  the  recognition  marks  and  calls 
by  which  the  different  members  of  the  species  know  each  other,  and 
that  have  the  corresponding  instincts  leading  them  to  associate  with 
their  own  kind.  I  have  elsewhere  called  this  principle  of  social 
coordination  "social  selection,"  and  have  classed  it  as  a  form  of 
reflexive  selection. 

2.  The  Cessation  of  Reflexive  Selection  between  Isolated  Sections  Causes 
Divergence  as  Soon  as  Heredity  Weakens. 

Independent  breeding  is  in  its  very  nature  the  suspension,  not  only 
of  one  form,  but  of  all  forms  of  reflexive  selection  between  the  separated 
portions  of  the  species.  The  importance  of  the  cessation  of  natural 
selection  in  producing  the  different  stages  of  the  degeneration  of  organs 
that  are  disappearing  has  been  fully  discussed  by  Professor  Romanes 
(see  Nature,  vol.  xli,  p.  437,  and  previous  communications  there  re- 
ferred to),  who  points  out  that,  as  the  power  of  the  special  form  of 
heredity  by  which  any  organ  is  produced  has  been  built  up  by  the 
many  generations  of  natural  selection  that  have  acted  on  the  organ,  so 
the  gradual  weakening  of  that  power  follows  the  cessation  of  the  natu- 
ral selection.     Professor  Weismann  seems  to  appeal  to  the  same  prin- 


ARE    SPECIFIC    CHARACTERS    ALWAYS    USEFUL?  255 

ciple  when  he  attributes  the  disappearance  of  "rudimentary  organs" 
to  the  action  of  "panmixia."  Now,  in  the  cessation  of  reflexive  selec- 
tion which  follows  independent  breeding,  a  similar  principle  is  intro- 
duced, and  the  inevitable  result  must  be  the  weakening  of  the  power 
of  heredity  by  which  the  portions  of  the  species  were  held  in  corre- 
spondence with  each  other  before  their  separation.  I  have  elsewhere 
shown  that  separate  breeding  necessarily  disturbs  unstable  adjust- 
ments ;  and  we  here  see  that  the  most  stable  of  the  adjustments  by 
which  each  part  of  a  species  is  kept  in  correspondence  with  every 
other  part  gradually  becomes  unstable  under  the  continued  influence 
of  separation.  Whenever  a  species  is  divided  into  two  portions  that 
do  not  interbreed,  the  forms  of  reflexive  selection  will  cease  to  act 
between  the  two  portions,  and  they  will  continue  in  sexual,  social, 
and  other  forms  of  harmony  with  each  other  only  in  so  far  as  the 
force  of  the  old  heredity  holds  them  to  the  old  standards.  But  the 
power  of  heredity  in  these  respects  will  in  time  fail,  and  if  the  sep- 
arate breeding  is  long  continued,  incompatibility  in  all  these  respects 
tends  gradually  to  arise.  Moreover,  it  is  manifest  that  incompatibil- 
ity of  industrial  habits  involving  diversity  in  the  forms  of  active  (or 
endonomic)  selection  will  in  time  arise.  I  therefore  maintain  that 
separation,  which  necessarily  includes  cessation  of  reflexive  selection 
between  the  portions  separated,  is  a  cause  of  segregation  and  diver- 
gence ;  and  that  this  segregation  is  in  time  intensified  by  diversity  of 
environal  selection,  through  diversity  in  the  use  of  the  environment. 

Unless  the  separated  portions  of  a  species  possess  exactly  the  same 
average  character  (which  we  must  believe  is  seldom,  if  ever,  the  case), 
separation  must,  from  the  first,  be  more  or  less  segregative ;  and  even 
in  cases  where  the  portions  completely  correspond  in  character  (if 
there  are  any  such  cases),  the  cessation  of  reflexive  selection  which  is 
involved  in  the  separate  breeding  must  result  in  divergence  as  soon  as  the 
power  of  heredity  securing  the  original  adjustments  begins  to  weaken;  and 
this  is  in  due  time  followed  by  other  forms  of  intensive  segregation.  I 
therefore  conclude  that  indiscriminate  separation  may  be  regarded  as 
a  preliminary  form  of  segregation  (that  is,  as  demarcational  segrega- 
tion) and  that  intensive  segregation  cooperating  with  this  produces 
complete  segregation. 

IV.  The  Utiuty  of  Specific  Characters.* 

I  have  followed  the  discussion  on  the  utility  of  specific  characters 
with  great  interest;  and  though  I  am  at  such  a  distance  that  my 
thoughts  may  come  a  little  late,  I  wish  to  call  attention  to  a  few  points. 

*  Published  in  Nature,  April  i,  1897. 


256  APPENDIX   III — LETTERS   PUBLISHED   IN    NATURE. 

In  Nature  for  October  22,  1896,  page  605,  mention  is  made  of  a  dis- 
cussion on  Neo-Lamarckism  at  the  British  Association.  In  opening 
the  discussion,  Prof.  Lloyd  Morgan  referred  to  the  importance  of 
noting  the  bearing  of  certain  cases  that  may  be  considered  as  crucial, 
or  as  nearly  crucial  as  any  that  we  are  at  present  able  to  obtain,  on 
the  process  by  which  specific  instincts  are  built  up.  As  illustrating 
this  class  of  cases,  he  refers  to  the  drinking  instinct  in  newly  hatched 
chickens,  where  the  instinctive  response  begins  at  the  point  where  the 
teaching  of  the  parent  bird  would  naturally  be  inadequate. 

The  question  I  wish  to  raise  is  whether  such  observations  as  this 
can  do  more  than  justify  the  conclusion  that  life-saving  instincts  are 
strengthened  and  established  by  natural  selection.  Are  they  suffi- 
cient to  show  that  all  permanently  inheritable  specific  characters  are 
wholly  due  to  natural  selection,  or  even  that  natural  selection  is 
always  one  of  the  factors  by  which  any  and  every  permanent  character 
has  been  built  up  ?  It  seems  to  me  that  there  are  large  classes  of  facts, 
some  of  which  may  be  found  in  almost  every  species  we  examine, 
which  throw  doubt  upon  there  being  any  such  inseparable  connection 
between  natural  selection  and  the  inheritance  of  characters. 

1.  Right-handedness  and  Left-handedness. 

The  majority  of  the  human  species  inherit  right-handedness.  Does 
this  prove  that  right-handedness  is  better  for  the  race  than  left- 
handedness?  The  shells  of  most  snails  are  coiled  in  a  way  that  is 
called  dextral ;  but  some  groups  of  species  are  as  constantly  sinistral 
as  most  groups  are  dextral ;  and  of  the  dextral  groups  there  are  cer- 
tain species  that  are  persistently  sinistral;  others  that  are  nearly 
equally  divided  between  dextral  and  sinistral  forms.  Is  it  necessary 
to  believe  that  for  each  species  that  is  usually  either  dextral  or  sinistral 
there  is  some  vital  necessity  that  would  exterminate,  or  even  dimin- 
ish, the  species  if  the  character  was  reversed?  A  similar  class  of 
cases  is  found  amongst  the  different  species  of  flatfish.  One  species 
persistently  lies  on  the  right  side,  another  on  the  left,  and  I  think  it  is 
Mr.  Cunningham  who  has  told  the  readers  of  Nature  that  there  are 
some  species  in  which  both  forms  may  occur.  In  each  of  these  classes 
of  cases  I  am  unable  to  conceive  of  any  advantage  gained  by  the 
species  that  would  not  be  equally  gained  if  the  character  under  dis- 
cussion was  reversed.  //  the  adaptation  to  the  environment  of  a  flat- 
fish that  now  lies  upon  the  right  side  would  he  equally  good  in  case  all  the 
individuals  of  the  species  lay  upon  the  left  side,  then  (if  I  rightly  under- 
stand the  meaning  of  the  terms) ,  natural  selection  can  not  be  the  cause  of 
its  lying  on  the  right  side  rather  than  the  left,  neither  can  this  character  of 


RIGHT-HANDEDNESS   AND   LEFT-HAHDEDNESS.  257 

the  species  be  considered  a  useful  character,  though  it  is  persistently 
inherited. 

Standing  near  me  is  a  flower-pot,  in  which  are  several  stalks  of  the 
common  calla  (I  believe  the  botanical  name  is  Richardia  cethiopica)  in 
bloom ;  and  a  little  inspection  shows  that  each  spathe  and  leaf-bud  is 
twisted  in  the  same  way.  If  the  leaf  is  held  with  the  point  up  and  the 
upper  surface  toward  you,  the  half  of  the  leaf  on  your  left  is  the  part 
that  formed  the  inside  of  the  leaf-bud,  and  the  margin  of  the  leaf  on 
your  right  is  the  part  that  formed  the  outside  of  the  leaf-bud.  This 
character  is  quite  persistent  in  the  specimens  of  this  species  found  in 
this  city,  though  I  am  told  that  a  leaf  twisted  in  the  opposite  way 
sometimes  appears ;  while  in  the  distinct  species  popularly  called  the 
black  calla  I  believe  the  character  is  reversed.  Now,  does  this 
persistence  prove  that  the  character  in  question  is  essential  to  the 
welfare  of  the  species?  Are  we  justified  in  assuming  that  natural 
selection  is  the  cause  of  the  persistence  of  such  characteristics  ?  Can 
anyone  throw  light  on  the  subject  that  will  make  it  easier  to  believe 
that  the  adaptation  of  the  species  would  be  in  the  least  impaired  if  all 
the  leaves  and  spathes  were  twisted  in  the  reverse  way? 

The  usual  method  of  meeting  the  natural  inference  from  such  cases  is 
based  on  a  double  assumption,  the  first  part  of  which  is  that  natural 
selection  is  the  only  intelligible  explanation  of  the  modification  of 
species  or  the  persistence  of  character  that  has  ever  been  given,  and 
that  if  in  any  case  we  abandon  this  explanation,  it  is  equivalent  to 
abandoning  all  explanation ;  the  second  part  of  the  assumption  being 
that  it  is  simply  our  ignorance  of  the  facts  that  prevents  us  from 
recognizing  the  life-preserving  results  that  are  gained  by  the  char- 
acteristic in  question.  This  assumption  ignores  both  the  fact  that 
species  presenting  characters  of  the  kind  referred  to  are  found  on 
every  side,  indeed  that  almost  every  species  that  fails  to  maintain  com- 
plete symmetry  of  form  is  an  example,  and  the  fact  that  Darwin  him- 
self pointed  out  another  principle  besides  natural  selection  producing 
persistent  characters.  This  principle  of  sexual  selection  he  carefully 
distinguished  from  natural  selection,  showing  that  the  results 
produced  by  it  could  never  be  produced  by  natural  selection,  and 
even  maintaining  that  "It  is  not  surprising  that  a  slightly  injurious 
character  should  have  been  thus  acquired."  (The  Descent  of  Man, 
2d  ed.,  p.  601.) 

For  my  part  I  do  not  think  much  progress  can  be  made  in  dis- 
covering where  natural  selection  is  the  chief  agent  and  where  it  is  not 
the  chief  agent  till  we  have  carefully  defined  what  we  mean  by  utility 
and  natural  selection,  and  then  adhere  to  our  definitions.     In  my 


258  APPENDIX   III — LETTERS   PUBLISHED   IN    NATURE. 

papers  on  "Divergent  Evolution  through  Cumulative  Segregation" 
and  "Intensive  Segregation"  I  have  endeavored  to  show  that  there 
must  be  several  principles  somewhat  similar  to  sexual  selection,  which 
I  have  grouped  with  it  under  the  names  reflexive  segregation  and 
reflexive  selection.  In  the  former  of  these  papers,  pages  212-214,  I 
have  pointed  out  that  of  freely  crossing  forms  of  any  species  it  is 
only  those  that  are  most  successful  that  are  perpetuated;  while  of 
forms  that  have  by  isolation  escaped  from  competition  with  the 
original  stock  and  are  not  crossing  with  it  every  variation  is  perpet- 
uated that  is  not  fatally  deficient  in  its  adaptations  to  the  environ- 
ment; and  this  will  be  the  case  whether  the  forms  are  held  apart  by 
reflexive  or  environal  segregation. 

2.  A  Difference  in  Use  that  is  not  a  Useful  Difference. 

Let  us  consider  the  case  of  two  allied  species  occupying  the  same 
area,  and  differing  from  each  other  in  what  Dr.  Wallace  has  so  appro- 
priately called  their  recognition  marks,  and  in  the  segregating  sexual 
and  social  instincts  correlated  with  these  marks.  If  investigation 
justifies  the  belief  that  an  early  stage  of  divergence,  due,  perhaps,  to 
local  segregation,  resulted  not  only  in  sexual  and  social  segregation, 
but  also  in  what  I  have  called  divergent  social  selection  (or  what  Dr. 
Wallace  prefers  to  call  selective  association),  then  we  are  warranted 
in  the  belief  that  this  segregative  and  selective  principle  was  sufficient 
to  perpetuate  and  intensify  the  new  character,  although  the  section  of 
the  species  possessing  the  new  character  had  not  migrated  into  any 
new  environment,  and  had  not  been  "exposed  to  any  change  in  the  old 
environment,  and  although  it  had  not  gained  any  new  adaptation  to 
the  common  environment  of  the  two  sections  and,  therefore,  while 
both  sections  of  the  species  were  equally  subject  to  identical  forms  of 
natural  selection. 

Now,  seeing  that  the  individuals  of  the  segregated  sections  are  able 
to  find  and  keep  company  with  associates,  and  in  the  season  to  pair 
with  suitable  mates,  as  effectually,  but  no  more  effectually,  than  be- 
fore they  were  segregated,  what  shall  we  say  of  the  usefulness  of  the 
distinctive  characters  that  produce  the  segregation?  It  is  plain  that 
these  divergent  characters  are  in  constant  use;  but  does  that  prove 
that  the  divergence  is  a  useful  divergence  ?  Is  it  not  possible  that  there 
should  he  a  difference  in  use  which  is  not  a  useful  difference?  And  if 
nothing  has  been  gained  by  the  difference  either  in  maintaining  the  con- 
ditions of  individual  life,  or  in  propagating  the  species,  how  can  we  call 
it  a  useful  difference?  And  how  can  we  attribute  the  divergence  to 
natural  selection,  seeing  that  natural  selection  is  the  superior  mainte- 


DIFFERENCE    IN    USE   AND   USEFUL   DIFFERENCE.  259 

nance  and  propagation  of  those  better  adapted  to  maintain  life  under 
the  conditions  surrounding  the  species? 

3.  Divergence  through  Reflexive  Selection  often  Non-advantageous. 

I  maintain  that  this  reflexive  segregation  through  the  sexual  and 
social  instincts  of  the  divergent  sections  of  the  species  is  the  first  in  a 
series  of  divergent  characters  which  may  become  a  great  advantage  to 
both  sections  of  the  species  by  enabling  them  to  become  adapted  to 
different  kinds  of  resources,  requiring  incompatible  adaptations ;  but 
it  can  not  be  claimed  that  the  usefulness  to  which  this  segregative 
character  may  attain  in  the  future,  or  may  have  already  attained,  was 
the  cause  of  the  divergence  which  was  steadily  perpetuated,  being  in- 
tensified by  sexual  and  social  selection,  and  so  completed  while  as  yet 
this  character  was  of  no  service  to  the  species.  The  segregative  char- 
acter is  preserved  by  its  segregativeness,  though  at  the  time  it  arises,  and  for 
many  subsequent  generations,  it  may  not  be  of  any  advantage  to  its  pos- 
sessors. In  most  such  cases,  I  believe,  the  initial  divergence  is  gained 
by  a  local  variety  in  some  measure  protected  by  local  segregation ; 
but  having  gained  a  character  which  secures  segregation,  even  when 
commingled  with  the  other  section  of  the  original  species,  it  is  no  longer 
liable  to  be  swamped  by  crossing.  It  seems  to  me  that  such  cases  arc 
examples  of  divergence,  produced  by  segregate  breeding,  brought 
about  by  sexual  and  social  segregation,  reinforced  and  strengthened 
by  sexual  and  social  selection,  and  not  by  diversity  in  the  action  of 
natural  selection. 

4.  Different  Methods  of  Using  the  Same  Resources  not  Necessarily  Advantageous. 

Another  fundamental  distinction  which  needs  to  be  kept  in  mind  is 
that  diversity  in  the  action  of  environal  selection  on  segregated  sec- 
tions of  a  species  may  be  due  to  three  classes  of  causes,  which  are  the 
real  causes  of  the  divergence,  which  results  in  the  production  of  dif- 
ferent species. 

(i)  Different  Hfe-supporting  and  life-endangering  conditions  exist- 
ing in  the  different  districts  in  which  the  different  sections  of  the  spe- 
cies are  distributed. 

(2)  Different  methods  of  using  resources  and  escaping  dangers 
adopted  by  the  different  sections,  though  occupying  the  same  district. 

(3)  Different  methods  of  using  resources  and  escaping  dangers 
adopted  by  the  different  sections  of  the  species  occupying  isolated 
districts,  whose  resources  and  dangers  are  alike. 

If  the  members  of  the  original  species  are  brought  under  the  influence 
of  the  first  class  of  causes,  the  divergence  is  due  to  diversity  in  the  en- 
vironments to  which  migration  introduces  them ;  if  under  the  second 


26o  APPENDIX   III — LETTRRS   PUBIJSHED   IN   NATURE. 

class,  it  is  due  to  diversity  in  the  action  of  life-preserving  habits  while 
at  the  beginning  of  the  process  competing  with  each  other;  if  under 
the  third  class,  it  is  due  to  diversity  in  life-preserving  habits  while  not 
competing  with  each  other. 

Now,  in  some  of  the  cases  in  the  second  class  and  in  all  those  of  the 
third  class,  it  is  impossible  that  the  differences  should  be  useful.  This 
is  most  easily  shown  as  regards  the  third  class ;  for  if  in  any  case  a  new 
character  attained  by  one  of  the  sections  is  an  advantage,  then  the 
same  character  would  be  an  advantage  for  each  of  the  other  sections, 
exposed  to  the  same  conditions  in  other  regions,  and,  therefore,  there 
is  no  advantage  in  the  difference. 

If  my  thought  is  correct,  some  of  the  differences  produced  by  diver- 
sity in  the  action  of  the  several  forms  of  reflexive  segregation  and  selec- 
tion, and  all  those  produced  by  diversity  in  the  action  of  environal 
selection,  when  that  diversity  is  due  to  different  habits  that  are  not 
necessitated  by  any  difference  in  the  environment,  are  non-useful  dif- 
ferences. Therefore,  besides  the  principle  of  "  correlated  variation  " 
referred  to  by  Professor  Lankester  (Nature,  vol.  liv,  pp.  245,  365),  we 
have  other  explanations  of  certain  kinds  of  specific  characters  that  are 
not  useful ;  but  the  class  of  characters  of  which  right-handedness  and 
left-handedness  are  examples  seem  to  lie  beyond  the  reach  of  these 
explanations,  and  perhaps  beyond  the  reach  of  the  explanation  sug- 
gested by  Professor  Lankester. 

5.  Letter  by  T.  D.  A.  Cockerell,  with  Suggestions  on  the  Facts  Mentioned  Above. 

The  following  letter  in  reply  to  the  above  appeared  in  Nature  for 
May  13,  1897: 

The  utility  of  specific  characters. 

Under  the  above  heading,  in  your  issue  of  April  i,  Mr.  J.  T.  Gulick  has  an  inter- 
esting communication,  in  which  he  asks  whether  it  is  possible  to  explain  right- 
handedness,  the  dextral  or  sinistral  coil  of  snail  shells,  and  similar  features,  as 
having  any  utility  of  which  they  are  certainly  characteristic.  Can  it  be  due  to 
natural  selection  that  one  snail  is  dextral  while  another  is  sinistral  ? 

It  is  a  curious  fact,  I  think,  first  pointed  out  by  Mr.  Call,  that  in  the  American 
fresh-water  shells  of  the  genus  Campeloma,  sinistral  shells  are  more  numerous 
among  the  young  than  among  the  adults.  Thus,  for  example,  Mr.  H.  A.  Pilsbry 
(Nautilus,  February,  1897,  p.  118),  states  that  Miss  Jennie  F.  Letson  examined 
a  lot  of  Campeloma  desisum  for  him,  with  the  result  that  out  of  681  specimens, 
mainly  adult,  but  including  those  from  one-fourth  grown  up,  none  were  sinistral. 
Out  of  410  shells  of  the  uterine  young  3  were  sinistral,  slightly  over  0.73  per  cent." 
He  adds:  "Probably  all  who  have  collected  Campelomas  have  noticed  the  greater 
proportion  of  sinistral  examples  among  the  young  shells.  This  doubtless  indi- 
cates that  the  reversed  condition  is  an  unfavorable  one  for  maturition." 

So  here,  at  any  rate,  we  have  some  direct  evidence  as  to  selection.  I  think  it 
will  strike  anyone    that  while  left-handedness  might  be  as  good  for  the  race  as 


DOES  ADVANTAGE  IN  UNIFORMITY  EXPLAIN  DIVERGENCE?       26 1 

right-handedness, /A^re  is  a  distinct  advantage  in  uniformity,  and  that  consideration 
alone  may  perhaps  suffice  to  explain  Mr.  GuHck's  difficulty.  Among  plants  it 
may  seem  less  obvious,  but  where  seedlings  are  crowded,  uniformity  may  save 
space,  just  as  a  number  of  objects  of  the  same  shape  can  usually  be  packed  into 
less  space  than  those  of  diverse  shapes.  More  plants  can  grow  in  a  window-box 
when  all  bend  to  the  light  than  would  be  possible  if  half  of  them  bent  one  way 
and  half  another. 

There  also  occurs  to  me  a  theoretical  consideration,  perhaps  of  doubtful  value. 
When  a  germ  has  diverse  potentiahties,  so  that  it  is  left  to  germinal  or  environ- 
mental selection  to  decide  which  course  it  shall  take  in  development,  there  must 
apparently  be  a  certain  waste  of  germinal  energy.  Any  disadvantage  thus  arising 
is  ordinarily  much  more  than  counterbalanced  by  the  gain  due  to  the  adapta- 
bility of  the  organism,  or  in  social  species  to  the  power  of  specialization  of  the  in- 
dividual for  social  purposes.  But  it  may  be  that  when  no  such  advantage  is 
found,  there  exists  a  small  disadvantage  in  deviations,  potential  or  axial,  from  a 
common  standard. 

What  we  really  need,  in  discussing  these  matters,  is  the  observation  of  actual 
facts.  The  facts  above  related  as  to  Campeloma  are  worth  more  than  any  amount 
of  theoretical  considerations. 

T.  D.  A.  COCKERELU. 

Mesilla,  New  Mexico,  U.  S.  A.,  April  21,  1897. 

6.  Reply  to  Letter  of  T.D.  A.  Cockerell. 

The  advantage  in  uniformity  is  very  manifest  in  certain  cases;  and,  on  pages 
68-70  of  this  volume,  I  refer  to  conditions  in  which  it  is  more  manifest  than  in 
the  cases  here  suggested  by  Mr.  Cockerell;  but  the  advantage  of  uniformity 
does  not  "explain  the  difficulty"  I  have  raised.  For  how  can  the  advantage 
of  uniformity  explain  the  introduction  of  permanent  diversity  through  the  sur- 
vival of  a  variation  that  breaks  down  the  former  uniformity,  and  establishes  two 
forms  where  there  was  a  single  form  ? 

The  disadvantage  in  deviation  from  a  common  standard,  if  it  can  be  shown  to 
be  a  fact,  is  perhaps  akin  to  the  fact  that  variations  most  widely  diverging  from 
the  average  form  are  usually  less  fertile.  But  how  can  the  advantage  of  a  com- 
mon standard  cause  the  dividing  of  a  species  according  to  two  different  standards 
as  in  the  case  of  some  snails?  For  any  one  snail  of  a  dextral  group  there  may  be  a 
disadvantage  in  being  of  a  sinistral  form;  but  does  that  throw  any  light  on  why  a 
species  should,  under  one  environment,  divide  itself  into  two  groups,  one  being 
dextral  and  the  other  sinistral?  and  does  it  show  that  the  process  is  due  to  nat- 
ural selection?     The  best  explanation  I  can  suggest  is  given  on  pages  68-70. 

J.  T.  GuucK. 


APPENDIX  IV. 
LIST  OF  PAPERS  ON   EVOLUTION  BY  JOHN  T.  GULICK. 

An  article  published  in  Nature,  July  i8,  1872,  entitled: — 

The  Variation  of  Species  as  related  to  their  Geographical  Distribution,  illustrated 
by  the  Achatinellince. 

Three  papers  published  in  the  Linnean  Society's  Journal,  Zoology,  vols,  xi, 
XX,  XXIII,  as  follows : 

Diversity  of  Evolution  under  One  Set  of  External  Conditions,  in  1872. 

Divergent  Evolution  through  Cumulative  Segregation,  in  1887;  reproduced  in  the 
Smithsonian  Report  for  1 89 1 ;  a  small  portion  of  the  same  is  also  given  in  Appendix 
I  of  this  volume. 

Intensive  Segregation,  in  1889;  reproduced  in  Appendix  II  of  this  volume. 

Three  articles  published  in  the  American  Journal  of  Science  for  January,  July, 
and  December,  1 890,  as  follows : 

Divergent  Evolution  and  the  Darwinian  Theory. 

The  Inconsistencies  of  Utilitarianism  as  the  exclusive  Theory  of  Evolution. 

The  Preservation  and  Accumulation  of  Cross-Infertility. 

Four  letters  published  in  Nature,  and  reproduced  in  Appendix  III  of  this 
volume. 

262 


INDEX 


Accommodation,  30,  158,  189. 

As  Acquired  Adjustment,  57,  60. 

Necessary  in  Case  of  Sudden  Change,  60,  62. 

Gives  Time  for ' '  Coincident  Variation, "  6 1 ,62. 

Controls  other  Influences,  61. 

Supersedes  Natural  Selection,  61. 

In  Man  Illustrated,  61,  152. 

May  Prevent  Coincident  Selection,  63. 

Forms  of  Accommodation,  153. 
Acquired  Characters: 

May  Influence  Racial  Characters,  20-22,  45, 
153. 

Through  Different  Habits  of  Feeding,  20. 

Habit  may  Control  Selection,  21. 

Often  Leads  to  "Coincident  Variation,"  21. 

And  Segregate  Association,  45,  48. 

Selection  and  the  Inheritance  of,  78. 

Inheritance  of.  Discussed  by  Cunningham,  78. 
By  C.  B.  Davenport.  78. 
Achatinellida: 

Illustrating  Problems  in  Evolution,  37-43. 

Two  Hundred   Species,    1,000  Varieties,   on 
Oahu,  39. 

Distribution  of  the  Genera.  37,  40,  42. 
Adaptation; 

As  Inherited  Adjustment,  56. 

Segregate  Adaptation,  87. 
Adjustment: 

Acquired  by  the  Individual  is  Accommoda- 
tion, 60. 

When  Inherited  is  Adaptation,  60. 
Agamic  Evolution  Defined,  137. 
AUogamic — 

Organisms,  79. 

Evolution  Resting  on  Six  Conditions,  79. 

Evolution  Defined,  137. 

Evolution  Controlled  by  Four  Principles,  138. 

Forms  of  the  Principles  of,  138. 
Amalgamation  of  Races,  20,  151,  188,  211. 
Anticipatory  Action,  29-30,  158. 
Aptitudes: 

As  Inherited  Characters,  47. 

As  Inherited  Adaptation,  56,  60. 
Areas  of  Distribution: 

Of  Hawaiian  Snails,  1-3,  37-43. 

Of  Arboreal  Species  most  Limited,  2. 

Species  a  Few  Miles  Apart  do  not  Intergrade,2 
Autogamic — 

Evolution  Defined,  137. 

Mating  used  by  Karl  Pearson,  137. 
Autonomic — 

And  Heteronomic  Influences,   141-144;  also 
Preface. 


Autonomic — Continued. 

Influences  Include  Endonomicand  Reflexive, 

141. 
Selection  and  Isolation,  141. 
Election  and  Partition,  142. 
Demarcation,    Intensification,    Segregation, 

142. 
Partition  and   Isolation  Illustrated,  143-144. 
Factors,  158. 

Darwin  Recognized  One,  158. 
Baldwin,  J.  Mcrk: 

"Organic  Selection,"  46,  61. 
Use  of  the  Term  "Selection,"  46. 
Control  of  Evolution,  49. 
"Social  and  Ethical  Interpretations,"  46,142. 
"Development  and  Evolution,"  30,   50,  53, 
61,  189. 
Bateson, ' '  Material  for  the  Study  of  Variation,  "34. 
Considers  Discontinuity  of  Species  as  Un- 
solved, 36. 

As  Inconsistent  with  Theories  of  Dar- 
win and  Lamarck,  .^4. 
Biometrika,  154. 
Bionomic  Laws,  9-22. 

Method  of  Their  Investigation,  9-13. 
Bionomics: 

Defined,  9. 

As  Taught  by  Distribution  of  Species,  10. 
The  Principles  Involved  in  Relations  of  Spe- 
cies, 1 1 . 
"Like to  Like,"  Fundamental  in  Bionomics, 
245-249. 
Blubber  Protects  the  Eskimo,  62. 
Broca,  "  Human  Hybridity,"  166. 
Brooks,  W.  K.,  Variability  of   Males  and  of  Spe- 
cies, 190. 
Bumpus,  H.  C,  on  Statistics  Proving  Selection,  34. 
Castes,  New,  being  Formed  in  India,  143,  153. 
Cats  of  Aquatic  Habits,  Illustrating  Influence  of 

Habitudes  on  Aptitudes,  67-68. 
Cockerell,  T.  D.  A.: 

On  Utility  of  Specific  Characters,  260-261. 
The  Author's  Reply  to  the  Same,  261. 
Coincident  Selection,  61. 
Coincident  Variation,  61,  62. 
Computation — 

Of  Ratio  of  Cross-breeds  to  Pure-breeds,  103- 
106. 

Compared   with    Endowment   Lessened 
by  Taxation,  103-104. 
Of  Negative  and  Positive  Segregation,  Co- 
operating, 101-111. 
Of  Cumulative  Segregation  in  Plant  Species, 
108-111. 

263 


264 


INDEX. 


Computation — Continued. 

Of  cumulative  segregation,  etc. — Continued. 
Direct,  in  a  Given  Case,  109. 
By  Table  A  in  a  Given  Case,  109. 
By  Table  V  in  a  Given  Case,  109. 
Of  Ratio  of  Half-breeds  to  Pure-breeds,  177- 

183. 
Of  Effects  of  Indiscriminate  Elimination,  210. 
Of  Probability  of  Mismating  without  Segre- 
gative Instincts,  99,  24 1 . 
Of  Probability  of  Mismating  given  in  Permu- 

tational  Triangle,  243. 
Of  Permutational  Triangle,  241-242. 
Conn,  Prof.  H.  W.,  "The  Method   of  Evolution," 

36.  145. 
Cope,  E.  D.: 

Retarded  and  Accelerated  Inheritance,  189. 
"Origin  of  the  Fittest,"  190 
Control  by  the  Organism: 

Of  Segregation  and  Divergence,  37-43,    1 15- 

127. 
Increases  with  Stage  of  Evolution,  156-157. 
Cooperation,  29,  158. 
Coulter,   John    M.,    "Plant   Structures,"   "Plant 

Relations,"  89. 
Cosmic  Process: 

Not,  as  Huxley  says,  Opposed  to  Ethics,  157. 
Illustrated  by  the  Rising  and  Setting  Sun, 
157. 
Cumulative  Adaptation  through  Survival  of  the 

Fittest,  96-98. 
Cumulative  Effects    through   Repetition  in  each 

Generation,  150. 
Cumulative  Integration  or  Invigoration  through 

Amalgamation,  96-98. 
Cumulative  Multiplication  through  Predominance 

of  the  More  Fertile.  96-98. 
Cumulative  Segregation: 

N'ew  Possibilities  through  Segregation,  96-98. 
In  Plant  Species  with  Computation,  108-1 11. 
Producing    Divergent    Evolution,     159-183, 
262. 
Cunningham,  J.  T. : 

"Sexual  Dimorphism,"  78. 
Inheritance  of  Functional  Characters,  78. 
Dextral  and  Sinistral  Flatfish.  256. 
Darwin,  Charles,  6,  23,  25,  26,  34,  94,  96,  153,  197, 
237. 

"The  Voyage  of  the  Beagle,"  3. 

"  The  Origin  of  vSpecies,"  3,  10,  26,  167,  215, 

253. 
"Variation  under  Domestication,"  167. 
"Cross-  and  Self-Fertilization,"  167. 
Present  Use  of  Isolation  not  the  Same  as  His, 

185. 
"Descent  of  Man,"  200. 
Divergence  Due  to  Environment,  216,  253. 
Sexual  Selection  Sometimes  Non-utilitarian, 
256. 
Davenport,  C.  B.: 

"Experimental  Morphology,"  78. 
Inheritance  of  Acquired  Characters,  78. 
Statistical  Methods,  154. 


Degeneration: 

Through  Cessation  of  Selection,  73-76. 
Illustrated  by  the  English  Cuckoo,  74. 
Illustrated  by  the  American  Cowbird,  74. 
In  Human  Eyesight,  74-75. 
In  the  Ani  and  Other  American  Birds,  75-76. 
DeVries,  Hugo: 

"Origin  of  Species"  in  Popular  Science,  70. 
Mutation,  70. 

"Species    and    Varieties;  Their    Origin    by 
Mutation,"  77. 
Dextral  and  Sinistral  Snails,  68-70. 
Discontinuity  of  Species,  34-36. 
Explained  by  Segregation,  35. 
Discussed  by  Professor  Conn,  36. 
Discriminate — 

And    Indiscriminate    Modes    of    Action,    80, 

132-136. 
Success  equals  Election,  53,  136. 
Survival  equals  Selection,  53,  136,  150. 
And  Indiscriminate  Isolation,  150. 
Divergence — 

That  is  not  Due  to  Sexual  vSelection,  3. 
Nor  to  Natural  Selection,  4-5. 
Nor  in  Proportion  to  Difference  in  En- 
vironment, 4. 
Nor  Useful  to  the  Species,  4. 
But  Due  to  Habits  of  Feeding,  5. 
And  to  Isolation,  7. 
Due  to  Independent  Transformation,  17-19. 
Through  Isolation  and  Selection,  17. 
Through  Segregation,  i.  c.  Discriminate  Iso- 
lation, 17. 
Independent  Transformation  always  Diver- 
gent, 18. 
Through   Indiscriminate    Destruction    under 

Isolation,  19. 
Through  Isolation  and  Variation,  29,  39, 
May  be  Lessened  by  Selection,  25,  29. 
Increased  by  Length  and  Degree  of  Isolation, 

27. 
Under  the  Same  Environment,  37-43. 
Through  Methods  of  Using  Resources,  39. 
Without  Advantage,  68-70. 
Utilitarian  and  Non-utilitarian.  194,  218. 
In  Land  Mollusks,  212-224. 
In  Snails  of  Oahu,  Hawaiian  Islands,  212. 
Without  Diverse  Environments,  215. 
In  Such  Cases  Without  Advantage,  217. 
Like  Divergence  in  Systems  of  Counting,  217. 
Not  Always  Adaptive,  218. 
Must  be  Advantageous  According  to  Thisel- 

ton  Dyer,  218. 
In  Proportion  to  Distance  of  Separation,  221 . 
Depending  on  Isolation  Illustrated,  222. 
In  Land  Snails  of  the  Society  Islands,  224. 
In  Insects,  225-234. 
In  Butterflies,  225-229. 
In  Periodical  Cicada,  229-234. 
Through  Cumulative  Segregation,  234-235  , 

262. 
Reply  to  Criticism  of  this  Theory,  236-240 . 
Not  Necessarily  Advantageous,  248. 


INDEX. 


265 


Divergence — Continued. 

In   Use  not   Necessarily   Useful   Divergence, 
258-260. 

Through    Refle.xive     Selection    not    Always 
Useful.  259. 

Not  Explained  by  Advantage  of  Uniformity, 
261. 

Under  One  Set  of  External  Conditions.  262. 
Domestic  Races; 

Reveal  the  Method  of  Evolution,  12. 

The  Production  of.  13-22. 

Their  Continuance,  13. 

Their  Transformation,  14. 

Their  Divergence,  17. 

Their  Stability,  19. 

Their  Amalgamation,  20. 

Affected  by  Acquired  Habits,  20-22. 

Adaptation  to  the  Rational  Environment.  13. 
Dominational  Selection  and  Election,  82,  86-87. 
Dyer,  W.  T.  Thiselton: 

Specific  Differences  Must  be  Advantageous, 
218. 

Are   Dextral   and   Sinistral    Forms    Advan- 
tageous, 218. 
Election: 

Need  of  Such  a  Term,  51. 

Defined,  53. 

As  Objectionable  as  Selection,  54. 

Its  Use  Must  be  Decided  by  Election,  55. 

Coincident,  Illustrated,  66. 

Reflexive,  81-114. 

Conjunctional.  82-83. 

Dominational,  82,  86-87. 

Institutional,  82,  1 14. 

Sexual,  83-84. 

Social,  83-85. 

Filio-parental,  83-86. 

Environal,  115-118. 

Endonomic,  115-118. 

Habitudinal,  115-118. 
Aptitudinal,  115-118. 
Heteronomic,  115-118. 
Natural,  115-118. 
Artificial,  115-118. 
Environal— 

Mode  of  Influence,  80,  1 15-129. 

Selection,  11.5-118. 

Isolation,  115-128. 

Election,  115-118. 

Partition.  115-129. 
Eskimo,  the,  Protected  by  Blubber,  62. 
Evolution: 

Of  Habitudes,  46,  48. 

Of  Race,  47. 

Determinate,  of  Terminology,  50. 

Controlled  by  the  Organism,  46,  49,  156,  158. 

Six  Conditions  for  Racial,  79. 

Six  Conditions  for  Habitudinal,  80. 

Determinate,  of  Animals,  158. 

Divergent,  159-183,  262. 

Monotypic,  of  Eight  Forms,  187-188. 

Monotypic  and  Polytypic,  198. 

Divergent,  and  Darwinian  Theory,  262. 

Inconsistencies  of  Utilitarianism  in,  262. 


Evolution,  Papers  on,  by  John  T.  GuHck,  262. 

Fecundal  Selection,  90-95. 

In  Human  Races,  92. 

Equals  Pearson's  "Reproductive  Selection," 
92. 
Filio-parental  .Selection,  83. 

.\nd  Big  Heads,  86. 

And  the  Normal  Number  of  Offspring,  91-92. 
Free  Crossing  Within  the  Group  a  Condition  of 

Evolution,  79. 
Formula  (1),  181. 
Formula  (2),  181. 

Used  in  Constructing  Table  V,  182. 
Formula  (3).  105. 

Formula  (4),  Used  in  Making  Table  A,  105. 
Four  Principles  of  Segregation,  The: 

Analysis  of,  79-136. 

Chief  Divisions  of,  79-81. 

The  Modes  of,  80. 

Classification  of  the  Forms  of,  137-143. 
Gallon,  Francis: 

"Possible     Improvement     of    the      Human 
Breed,"  113. 

Statistical  Methods,  154. 

"  Types  and  Their  Inheritance,"  186. 
Giddings,  Franklin  H.,  Control  of  Evolution,  49. 
Habitudes: 

As  Acquired  Characters,  48. 

As  Traditional   Forms   of   Accommodation, 
57,  60. 

Influencing  Aptitudes,  57,  67. 
Hawaiian  Snails,  Evolution  of: 

Their  Distribution,  1-3,  26-29. 

Small  Areas  of  Distribution,  1,  26. 

Areas  of  Arboreal  Species  Smallest,  2. 

Divergence  in  Different  Valleys,  2,  26. 

Diversity  of  Selection  Insufficient  Explana- 
tion, 27. 

Isolation  and  Variation  Essential  Factors,  29- 

Community  of  Descent  Secures  Unity,  29. 

Ten   Genera   of   Achatinellidae,    Illustrated, 
37-43. 
Headley.  F.  W.: 

"Problems  of  Evolution,"  46,  52,  55,  56. 

Selection  Controlled  by  the  Organism,  46. 

Criticism  of  Intensive  Segregation,  55-56. 
Heredity: 

And  Tradition,  46,  51,  58. 

Molding  of  Heredity  and  Variation,  60. 

Aptitudes   as   Inherited   forms   of  Adaptive 
Variation.  60. 

A  Condition  of  Evolution,  79. 

As  Fundamental  as  Variation,  79. 
Heteronomic — 

Influences,  141-142. 

Selection  and  Isolation,  141. 

Election  and  Partition,  142. 

Demarcation,    Intensification,    Segregation, 
142. 

Factors  were  Emphasized  by  Darwin,  158. 
Huxley,  T.   H.,   Ethics  Opposed  to  the  Cosmic 
Proces':,  157. 


266 


INDEX. 


Hyatt,  ■Mpheus.  192. 

Methods  of  Studying  Segregation,  154. 

Earlier  and  Earlier  Inheritance,  189. 

Decline  in  Individual  and  in  Type,  190. 
Impregnational  Isolation: 

And  Selection,  82,  87-111. 

Importance  of,  95-101. 

I  ndiscriminatc — 

Mode  of  the  Four  Principles,  132-136. 

Survival,  133. 

Equals  Indiscriminate  Elimination,  136,  152, 
209. 

Isolation,  133,  150,  152,  186,  252-255. 

Success,   134,  equals  Indiscriminate  Failure, 
136. 

Partition,  134. 

Contrast    in  Discriminate    and     Indiscrimi- 
nate Action,  134-136,  150. 

Table   of    Discriminate    and    Indiscriminate 
Forms,  136. 

Elimination,  Computation  Showing  Effect  of, 
210. 
Individual  Variations: 

Considered    of   no    Effect    by    Mutationists, 
71-77. 

Importance  of.  Shown,  73-77. 

And  Degeneracy  of  Eyesight,  74—75. 

And  Degeneracy  in  Cuckoo,  75-76. 

And  Degeneracy  in  Milk  Giving,  74. 

Selection  of.  Leads  to  Mutation,  77. 
Innovation: 

And  Variation,  46,  5 1 ,  59. 

Molding  of  Innovation  and  Tradition.  60. 

Intension: 

The  Law  of,  192-194. 

Selectional,  195-209. 

Indiscriminate  Eliminational,   209-211. 

Computation  of  Indiscriminate  Elimination, 

210. 
Amalgamational,  211. 

Equals  Intensive  Segregation,  185-243,  262. 
Isolation: 

In  Its  Broader  Meaning,  6. 

And  Divergent  Evolution,  7. 

Considered  by  Lamarck  and  Packard,  7. 

With  Variation  Causes  Divergence,  29. 

Importance  of,  51. 

Defined,  53. 

Coincident,  66-67. 

Caused  bv  Partition,  67-68. 

Structural,  68-70. 

Reflexive,  81-114. 

Conjunctional,  82-83. 

Impregnational,  82,  87-111. 

Institutional,  82.  114. 
'  Sexual,  83-84. 

Social,  83-85. 

Family,  86. 

Dimensional,  87-88. 

Structural,  87-89. 

Potential.  87,  89-90,  108-111. 


Isolation — Continued. 

Environal,  115,  118-128. 

Endonomic,  115,  118-122. 

Industrial,  115,  119-123. 
Chronal,  115,  123-125. 

Seasonal,  115,  124-125. 
Cyclical,  115,  123-124. 
Migrational.  115,  126-127. 
Heteronomic,  115,  118,  126,  128. 
Transportational,  115,  126. 
Geological,  115,  126. 
Fertilizational,  115,  128. 
Artificial,  115,  128. 
Spatial,  125. 
Geographical,  125. 
Local.  125. 
Unbalanced,  149. 

Usuafly  Somewhat  Discriminate,  174. 
Principles  Intensifying  Segregation,  174. 
Use  of,  and  Segregation,  175. 
As  Used  by  Darwin  and  as  Now  Used.  185. 
Indiscriminate,  of  a  Few  Segregative,  186. 
And   Unusual  Opportunities  for  Migra- 
tion, 221. 
And  Unstable  Adjustments,  249-252. 
Jennings,  Herbert  S.,  "Contributions  to  the  Study 

of  the  Behavior  of  Lower  Organisms,"  189. 
Jevons,  W.  S.,  "Principles  of  Science,"  210. 
Jones,  Rev.  J.  P.,  The  Formation  of  New  Castes 

in  India,  143. 
Jones,  Lynds: 

Accommodation  in  Birds,  64. 
Degeneracy  in  Nesting  Habits.  76. 
Kidd,  Benjamin,  "Principles  of  Western  Civiliza- 
tion," 30. 
Lamarck,  7,  34. 
Lankester,  Prof.  E.  Ray,  9. 

On  "Like  to  Like"  as  a  Principle,  245-248. 
Correlated  Variation,  260. 
Le  Conte,  Joseph,  215. 

Marlatt,  C.  L.,  On  the  Periodical  Cicada,  124. 
Mayer,  A.  G.: 

Dextral  and  Sinistral  Partulse,  70. 
"A  vStudy  in  Variation  of  Partula,"  155-156. 
Modes: 

Of  the  Four  Principles,  80. 
Environal,  of  Influence,  80,  1 15-129. 
Reflexive  Mode  of  Influence,  80-1 14. 
Regressive  Mode  of  the  Principles,  129-131. 
Discriminate     and     Indiscriminate     Modes. 
132-136. 
Morgan,  C.  Lloyd,  45,  189. 

"Habit  and  Instinct,"  21,  61. 
"Coincident  Variation,"  61. 
"Animal  Behavior,"  61. 

Natural  Selection  of  Innate  Characters.  256. 
Morgan,  T.  H.: 

"Evolution  and  Adaptation,"  71,  73. 
On  Mutations,  71-73. 
Mutation,  70-77. 

And  Varieties,  71. 

Expounded  by  T.  H.  Morgan,  71-73. 

Theory  Loses  Sight  of  Certain  Facts,  73-77. 


INDEX. 


267 


Mutation — Continued. 

Denies  Effect  of  Individual  Variation,  71-77. 
Reached  by  Selection  of  Fluctuating  Varia- 
tions. 77. 
Natural  Species: 

Evolution  of,  23-36,  212-240 

Unity  and  Diversity,  23-29. 

Unity    Through    Community    of     Descent, 

23-26. 
Diversity  not  Always   Through  Diversity  of 

Environments,  23-29. 
Selection  May  Help  tJnity  or  Diversity,  25,  29. 
May   Lose   Plasticity  and   Become   Extinct, 

212. 
Varieties  are  Incipient  Species,  213. 
Illustration   of   Intergrading   Species,    Plate 

111,43. 
Reference  to  Intergrading  Species,  214. 
Utility  of  Specific  Characters,  255-261. 
If  All  Men  were  Left-handed  no  Loss,  256- 

257. 
Many  Examples  of  Asymmetry,  257. 
Cockerell's  Letter  on  Utility  of  Specific  Char- 
acters, 260. 
Osborn,  H.  P.,  45;  also  Preface. 
Packard,  A.  S. ," Lamarck ;  His  Life  and  Work,"  7. 

Recognizes  Importance  of  Isolation,  7. 
Partition: 

Need  of  Such  a  Term,  51. 
Defined,  53. 

Industrial,  illustrated,  67. 
Reflexive,  81-114. 
Conjunctional,  82-83. 
Institutional,  82,  1 14. 
Family   83,  86. 
Social,  83-85. 
Environal,  115,  129. 

Endonomic,  115,  129. 
Industrial,  115,  129. 
Migrational,  115,  129. 
Heteronomic,  115,  129. 

Transportational,  115,  129. 
Geological,  115,  129 
Artificial,  115,  129. 
Pearson,  Karl: 

"The  Chances  of  Death,"  16,92-95,  113-114. 
"Grammar  of  Science,"  51,  92-94. 
Statistical  Methods,  154. 
Ph  y  siol  ogical — 

Isolation,  95-96. 
Selection,  96. 

Plate  A,  Map  of  Hawaiian  Islands,  between  42, 43. 
Plate  I,  Eight  Genera  of  Achatinellidae,  42,  43. 

Explanation  of,  37. 
Plate  B,  Map  of  Oahu,  42,  43. 

Explanation  of.  43. 

Plate  II,  Twenty-five  Species  of  Achatinella,  42, 
43, 

Explanation  of,  39. 

Plate   III,   Variation   and   Intergrading  of  Buli- 
raella,  42,  43. 

Explanation  of .  4 1 . 


Radius  of  Distribution  Varies — 

Directly  as  the  Power  for  Migrating,  220. 

Inversely  as  the  Power  for  Variation,  220. 
Rats  of  Arboreal  Habits,  as  Illustrating  Coopera- 
tion   of    Positive    and    Negative    Segregation, 
101-103. 
Reflexive — 

.Mode  of  Influence,  80-1 14. 

Selection,  81-114,  151. 

Isolation,  81-114. 

Election,  81-114. 

Partition,  81-114. 
Regressive — 

Mode  of  the  Four  Principles,  80,  129. 

Selection,  129,  131. 

Election,  129. 

Isolation,  130. 

Partition,  130. 
Reid,  G.  A.,  Increasing  Difficulty  of  Childbirth, 

86. 
Riley,  C.  V.,  Bui.  No.  8,  Divis.  Entomology,  U.  S. 

Department  Agriculture,  229-232. 
Romanes,  G.  J.,  192. 

"Darwin  and  After  Darwin,"  51   52. 

"Physiological  Isolation,"  52. 

On  Cessation  of  Natural  Selection,  198,  254. 

"Mental  Evolution  in  Animals,"  237-238. 
Scott,  William  E.  D. ,  How  Red-winged  Blackbird 

Learned  to  Crow,  84. 
Segregate  Adaptation,  87,  170. 

Association,  48;  also  Preface. 
Segregate  Generation,  47;  also  Preface. 

A  Condition  of  Allogamic  Evolution,  79. 
Segregate — 

Survival,  95-96,  108. 

Union,  95-96. 

Vigor,  87,  170. 

Escape  from  Enemies,  87,  171. 

Illustrated  by  Arboreal   Rats,  101    103. 

Fecundity,  87,  170. 

How  Accumulated,  262. 

Freedom  from  Competition,  87,  171. 

Illustrated  by  Arboreal  Rats,  101-103. 
Segregation: 

Its  Causes  and  Effects,  6-8. 

The  Fundamental  Process  in  Evolution,  8, 
22,  147,  151. 

Through  Transformation  During  Isolation,  8. 

Initial,  Through  Isolation,  22. 

Intensive,  Through  Transformation,  22. 

The  Four  Segregative  Principles,  45-78. 

Industrial,  45. 

Racial,  45,  47,  151. 

.Social  or  Habitudinal,  45.  48-49.  151,  153. 

Witiiout  it  Differences  Would  Cease,  47. 

Interaction  of  Racial  and  Social,  49. 

Four  Principles  of,  45-145. 

Interaction  of  the  Four  Principles,  55-78. 

Intensive,  and  Headley's  Criticism,  55-56. 

Importance  of  Each  of  the  Principles,  56-58. 

Impregnational,  illustrated,  68-70. 

Positive,  98-101,  163. 

Negative.  98-101.  163-164. 


268 


INDEX. 


Segregation — Continued. 

Negative  and  Positive,  Cooperating,  101-111, 
182-183. 

Cumulative,    Illustrated    in    Plant    Species, 
108-111. 

Intensifying,  151. 

Autonomic,  151. 

Control  of,  151,  156. 

Conditions  Favoring,  154. 

Favorable  Conditions  for,  in  Partula,  155. 

Reflexive,  159-183. 

Conjunctional,  159-163, 

Social,  160. 

Sexual,  160-162. 

Germinal,  162-163. 

Floral,  162-163. 

Impregnational,  163-171. 

Impregnational  Alone  is  Negative,   163. 

Dimensional,  165. 

Structural,  165. 

Potential,  166-170. 

How  Accumulated,  168. 

Institutional,  171. 

The     Importance  of     Impregnational,   172- 
174. 

Meaning  of  Isolation  and,  175. 

Forms  of,  1 76. 

Computation  of,  177-183. 

Intensive,  175-176.  185-243,  262. 

Forms  of  Intensive,  185-212. 

Forms  of,  Cooperate,  247-248. 

Divergent   Evolution   Through   Cumulative, 
159-183,  262. 
Selection: 

Not  Always  the  Cause  of  Divergence,  3-6. 

Divergence  that  is  not  Due  to  Sexual,  3. 
Nor  to  Natural,  4-5. 

Of  a  Species  Does  Not  Change  the  Species, 
14. 

Of  Other  Than  Average  Varieties  Produces 
Change,  15. 

When  Unbalanced  Produces  Change,  15. 

Conditioned  by  Fertility,  15. 

Of  Average  Forms  Tends  to  Stability,    16, 
195-196. 

Fecundal,  Due  to  Superior  Fertility,  16. 

May  Produce  Diversity  or  Unity,  25,  29. 

Diversity  of,  with  Isolation    Cau.ses  Diver- 
gence, 8,  22. 

How    Far    an    Explanation    of    Divergence, 
29-34. 

What  it  Does  Not  Explain,  29-31. 

How     Far    Determined    by    Environment, 
31-32. 

Endonomic,  One  Form  of  Autonomic,  32. 

May  be  Changed  Without  Change  in  Envi- 
ronment, 33. 

Statistical  Proof  of  Natural,  34. 

Reflexive,  36,  45. 

Active  and  Passive,  45. 

Headley  says.  May  be  Controlled  by  the  Or- 
ganism, 46. 


Selection — Continued. 
Defined,  53,  195. 

Coincident,  61,  63,  64,  65,  68,  152. 
Organic,  61,  62,  152. 
Endonomic,  in  Cliff  Swallows,  63. 
In  Chimney  Swift,  64. 
In  Tree  Swallow,  64. 
In  House  Wren,  64. 
In  Infants,  64. 
Defined,  65. 
And  Coincident,  65-67. 
Illustrated  by  Swimming  Cats,  67-68. 
Structural,  68-70. 
Reflexive,  82-114,  151,  197. 
Conjunctional,  82-83,  197. 
Dominational,  82,  86-87,  197,  203. 
Impregnational,  82,  87-111,  197,  206. 
Institutional,  82,  111-112,  153,  197,  207. 
Prudential,  82,  111-114,  153,  197,  207. 

By  which   Man  May  Control   His  Own 
.Evolution.  112,  153. 
Sexual,*  83-84,  200-202. 
Social,  83-84,  202-203. 
Filio-parental,  83,  86,  203. 

And  Lactation,  204. 
Dimensional,  87-88,  204-205. 
Structural,  87-89. 
Potential,  87,  89. 
Fecundal,  87,  90  -95,  206. 
Environal,  115-118,  196,  200 

Endonomic,  115-117,  152,  156,  197. 
Habitudinal,  115-117. 
Aptitudinal,  115-117. 
Heteronomic,  115,  117   118,  197. 
Natural,  115,  1,17-118. 
Artificial,    115,  117-118. 
Forms  of.  Defined,  139. 

Conditions  Determining  the  Forms  of,  140. 
Unwarranted  Assumption   Concerning   Nat- 
ural, 144-145. 
Unbalanced,  149. 
Cessation  of,  198. 
Rational  and  Adaptational,  199. 
Forms  of.  Classified.  199. 
Self-cumulative  Endowments,  96-98. 
Sexual — 

Election,  83-84. 
Isolation,  83-84. 
Selection,  83,  200-202. 

Darwin  says  Caused  by  Divergent  In- 
stincts ;  what  Causes  the  Latter,    1 1 , 
200. 
Explanation  given,  201. 
Illustrated  by  Creeping  Cricket,  200. 
Social — 

Election,  83,  85. 
Isolation,  83,  85. 
Partition,  83,  85. 
Selection,  83-84. 
Species: 

Intergrading  Between,  40-42. 
Statistical  Test  of,  40. 


*  See  under  Sexual. 


INDEX. 


269 


Spencer,  Herbert,  49. 

"Principles  of  Biology"  and   of  "Psychol 

ogy,"31. 
His  Fatalism  Based  on  Mistaken  Biology,  31. 
Uniform  Conditions  make  Uniform  Species, 

215. 

Stability  Through  Selection  of  Average  l'V)rins,  19. 
Statistical  Methods: 

In  Study  of  Fertility,  92-95. 
And  Place  Modes,  154. 
Success: 

Defined.  53. 

Discriminate,  equals  Election,  53,  136. 
Indiscriminate,  equals    Indiscriminate    Fail- 
ure, 136. 
Survival: 

Defined,  53. 

A  Condition  of  Evolution,  79. 
Segregate,  95-96.  ' 

Discriminate,  equals  Selection,  53.  136. 
Indiscriminate,  equals  Indiscriminate  Elimi- 
nation, 136. 
Table  A,  105. 

Used  in  a  Computation,  109. 
Table  I,  and  its  Formation,  177. 
Table  II,  and  its  Formation,  178. 
Table  III,  and  its  Formation,  179. 
Table  III,  and  its  Use,  180. 
Table  IV,  and  the  General  Formula,  181. 
Table  V,  182. 

Used  in  a  Computation,  1 09. 
Constructed  by  Formula  (2),  182. 
What  we  Learn  from  it,  182-183. 
Tables,  Use  of,  107. 
Tarde,  Gabriel,  "Social  Laws,"  50,  53. 
Tentative  or  Experimental — 

Variation  with^Survival,  30,  157. 
Accommodation,  158. 
Tradition,  48. 

And  Heredity,  46,  51,  58 
Molding  of  Tradition  and  Innovation,  60. 
Habitudes  as  Traditional  Forms  of  Accom- 
modation, 60. 
Transformation : 

Through  Unbalanced  Propagation,  15-17. 
By  Means  of  Selection,  15. 


Transformation — Continued. 

By  Means  of  Indiscriminate  Elimination,  16. 
Assimilational,  187. 
Stimulational,  187. 
vSuetudinal,  187. 
Emotional,  187. 
vSelectional,  188,  195   209. 
Indiscriminately  Eliminational,  188,209-211. 
.\malgamationa1,  188,  211. 
Fecundal,  188. 

During  Isolation  Divergent,  191. 
Unbalanced: 

Propagation,  148-149. 
Isolation,  149. 
Selection,  149. 
Upham,  Warren,  "Greenland  Icefields,"  62. 
Variation: 

And  Innovation,  46,  51,  59. 

Molding  of  Variation  and  Heredity,  60. 

Coincident  Variation,  61. 

Fluctuating,  with  Selection  Brings  Mutation, 

77. 
Functional,  Considered  by  Cunningham,  78. 
A  Condition  of  Evolution,  79. 
"vs.  Heredity, "by  Prof.  H.  S.  Williams,  79. 
And  Heredity  Equally  Fundamental,  79. 
Individual,  71-77. 

As    Related    to    Geographical    Distribution, 
262. 
Vernon,  H.  M.,  quotes  Bumpus,  34. 

"Variation  in  Animals  and  Plants,"  34. 
Wallace,  A.  R.,  4,  153. 

Criticism    of   Divergence   Through   Segrega- 
tion, 236-240. 
"Darwinism,"  245-246,  249-252. 
"Recognition  Marks"  and  Social  Selection, 
-       258. 
Ward,    Prof.   James,    "Naturalism   and   Agnosti- 
cism," 30. 
Ward,  Lester  F.,  Control  of  Evolution,  49. 
Weismann,  August: 

"Studies  in  the  Theory  of  Descent,"  215. 
And  "Panmixia,"  254. 
Whitworth,  "Choice  and  Chance,"  242. 
Williams.  Prof.  H.  S.,  "Variation  vs.  Heredity," 

79. 
Wright,  G.  Frederick,  "Greenland  Icefields,"  62. 


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